` `

Expresiones¶

The Expression string builder
Lista de funciones
Editor de Funciones

Based on layer data and prebuilt or user defined functions, Expressions offer a powerful way to manipulate attribute value, geometry and variables in order to dynamically change the geometry style, the content or position of the label, the value for diagram, the height of a composer item, select some features, create virtual field ...

The Expression string builder ¶

Main dialog to build expressions, the Expression string builder is available from many parts in QGIS and, can particularly be accessed when:

clicking the button;
selecting features with the ^{Select By Expression...} tool;
editing attributes with e.g. the ^{Field calculator} tool;
manipulating symbology, label or composer item parameters with the ^{Data defined override} tool (see Configuración de anulación definida por datos);
building a geometry generator symbol layer;
doing some geoprocessing.

The Expression builder dialog offers access to the:

Expression tab which, thanks to a list of predefined functions, helps to write and check the expression to use;
Function Editor tab which helps to extend the list of functions by creating custom ones.

Some use cases of expressions:

From Field Calculator, calculate a “pop_density” field using existing “total_pop” and “area_km2” fields:
```
"total_pop" / "area_km2"
```

Update the field “density_level” with categories according to the “pop_density” values:

CASE WHEN "pop_density" < 50 THEN 'Low population density'
     WHEN "pop_density" >= 50 and "pop_density" < 150 THEN 'Medium population density'
     WHEN "pop_density" >= 150 THEN 'High population density'
END

Apply a categorized style to all the features according to whether their average house price is smaller or higher than 10000€ per square metre:
```
"price_m2" > 10000
```
Using the “Select By Expression...” tool, select all the features representing areas of “High population density” and whose average house price is higher than 10000€ per square metre:
```
"density_level" = 'High population density' and "price_m2" > 10000
```
Likewise, the previous expression could also be used to define which features should be labeled or shown in the map.

Using expressions offers you a lot of possibilities.

Truco

Use named parameters to improve the expression reading

Some functions require many parameters to be set. The expression engine supports the use of named parameters. This means that instead of writing the cryptic expression clamp( 1, 2, 9), you can use clamp( min:=1, value:=2, max:=9). This also allows arguments to be switched, e.g. clamp( value:=2, max:=9, min:=1). Using named parameters helps clarify what the arguments for an expression function refer to, which is helpful when you are trying to interpret an expression at a later date!

Lista de funciones ¶

The Expression tab provides the main interface to write expressions using functions, layer’s fields and values. It contains widgets to:

type expressions using functions and/or fields. At the bottom of the dialog, is displayed the result of the expression evaluated on the first feature of the layer.
select the appropriate function among a list, organized in groups. A search box is available to filter the list and quickly find a particular function or field. Double-clicking on the item’s name adds it to the expression being written.
display help for each function selected. When a field is selected, this widget shows a sample of its values. Double-clicking a value adds it to the expression.

The Expression tab

Operadores ¶

This group contains operators (e.g., +, -, *). Note that for most of the mathematical functions below, if one of the inputs is NULL then the result is NULL.

Función	Descripción
a + b	Addition of two values (a plus b)
a - b	Subtraction of two values (a minus b).
a * b	Multiplication of two values (a multiplied by b)
a / b	División de dos valores (a dividido entre b)
a % b	Remainder of division of a by b (eg, 7 % 2 = 1, or 2 fits into 7 three times with remainder 1)
a ^ b	Power of two values (for example, 2^2=4 or 2^3=8)
a < b	Compares two values and evaluates to 1 if the left value is less than the right value (a is smaller than b)
a <= b	Compares two values and evaluates to 1 if the left value isless than or equal to the right value
a <> b	Compara dos valores y evalúa a 1 si no son iguales
a = b	Compara dos valores y evalúa a 1 si son iguales.
a != b	a and b are not equal
a > b	Compara dos valores y evalúa como 1 si el valor izquierdo es mayor que el valor derecho (a es mayor que b)
a >= b	Compara dos valores y evalúa a 1 si el valor de la izquierda es mayor que o igual que el valor de la derecha
a ~ b	a matches the regular expression b
\|\|	Joins two values together into a string. If one of the values is NULL the result will be NULL
‘\n’	Inserta una nueva línea en una cadena
LIKE	Devuelve 1 si el primer parámetro coincide con el patrón provisto
ILIKE	Returns 1 if the first parameter matches case-insensitive the supplied pattern (ILIKE can be used instead of LIKE to make the match case-insensitive)
a IS b	Tests whether two values are identical. Returns 1 if a is the same as b
a OR b	Returns 1 when condition a or condition b is true
a AND b	Returns 1 when conditions a and b are true
NOT	Niega una condición
column name “column name”	Value of the field column name, take care to not be confused with simple quote, see below
‘cadena’	a string value, take care to not be confused with double quote, see above
NULL	valor nulo
a IS NULL	a no tiene valor
a IS NOT NULL	a tiene valor
a IN (value[,value])	a esta debajo de los valores listados
a NOT IN (valor[,valor])	a no está debajo de los valores listados

Nota

About fields concatenation

You can concatenate strings using either || or +. The latter also means sum up expression. So if you have an integer (field or numeric value) this can be error prone. In this case, you should use ||. If you concatenate two string values, you can use both.

Algún ejemplo:

Une una cadena de texto y un valor de un nombre de columna:

'My feature''s id is: ' || "gid"
'My feature''s id is: ' + "gid" => triggers an error as gid is an integer
"country_name" + '(' + "country_code" + ')'
"country_name" || '(' || "country_code" || ')'

Test if the “description” attribute field starts with the ‘Hello’ string in the value (note the position of the % character):
```
"description" LIKE 'Hello%'
```

Conditionals ¶

Este grupo contiene funciones para menejar comprobaciones condicionales en expresiones.

Función	Descripción
CASE WHEN ... THEN ... END	Evalúa una expresión y devuelve un resultado si es verdadera. Puede probar múltiples condiciones
CASE WHEN ... THEN ... ELSE ... END	Evalúa una expresión y devuelva un resultado diferente sea verdadero o falso. Puede probar múltiples condiciones
coalesce	Devuelve el primer valor no-NULO de la lista de expresión
si	Prueba una condición y devuelve un resultado diferente dependiendo de la comprobación condicional
regexp_match	Returns true if any part of a string matches the supplied regular expression

Algún ejemplo:

Send back a value if the first condition is true, else another value:
```
CASE WHEN "software" LIKE '%QGIS%' THEN 'QGIS' ELSE 'Other' END
```

Funciones Matemáticas ¶

Este grupo contiene funciones matemáticas,por ejemplo raíz cuadrada, seno y coseno

Función	Descripción
abs	Devuelve el valor absoluto de un número
arcos	Devuelve la inversa del coseno de un valor en radianes
arcsen	Devuelve la inversa del seno de un valor en radianes
atan	Returns the inverse tangent of a value in radians
atan2(y,x)	Returns the inverse tangent of y/x by using the signs of the two arguments to determine the quadrant of the result
azimuth(a,b)	Returns the north-based azimuth as the angle in radians measured clockwise from the vertical on point a to point b
ceil	Rounds a number upwards
clamp	Restricts an input value to a specified range
cos	Devuelve el coseno de un valor en radianes
grados	Convierte de radianes a grados
exp	Devuelve la exponencial de un valor
floor	Rounds a number downwards
ln	Returns the natural logarithm of the passed expression
log	Returns the value of the logarithm of the passed value and base
log10	Returns the value of the base 10 logarithm of the passed expression
máx	Returns the largest value in a set of values
mín	Returns the smallest value in a set of values
pi	Returns the value of pi for calculations
radianes	Convierte de grados a radianes
rand	Returns the random integer within the range specified by the minimum and maximum argument (inclusive)
randf	Returns the random float within the range specified by the minimum and maximum argument (inclusive)
round	Rounds to number of decimal places
scale_exp	Transforma un valor dado de un dominio de entrada a un rango de salida usando una curva exponencial
scale_linear	Transforma un valor dado de un dominio de entrada a un rango de salida usando interpolación lineal
sen	Returns the sine of an angle
raíz cuadrada	Returns the square root of a value
tan	Devuelve la tangente de un ángulo

Aggregates Functions ¶

This group contains functions which aggregate values over layers and fields.

Función	Descripción
agregar	Returns an aggregate value calculated using features from another layer
concatenar	Returns the all aggregated strings from a field or expression joined by a delimiter
Número	Returns the count of matching features
count_distinct	Returns the count of distinct values
count_missing	Returns the count of missing (null) values
iqr	Returns the calculated inter quartile range from a field or expression
mayoría	Returns the aggregate majority of values (most commonly occurring value) from a field or expression
max_length	Returns the maximum length of strings from a field or expression
máximo	Returns the aggregate maximum value from a field or expression
media	Returns the aggregate mean value from a field or expression
mediana	Returns the aggregate median value from a field or expression
min_length	Returns the minimum length of strings from a field or expression
mínimo	Returns the aggregate minimum value from a field or expression
minoría	Returns the aggregate minority of values (least commonly occurring value) from a field or expression
q1	Returns the calculated first quartile from a field or expression
q3	Devuelve el tercer cuartil calculado a partir de un campo o expresión
intervalo	Returns the aggregate range of values (maximum - minimum) from a field or expression
relation_aggregate	Returns an aggregate value calculated using all matching child features from a layer relation
stdev	Returns the aggregate standard deviation value from a field or expression
sum	Returns the aggregate summed value from a field or expression

Ejemplos:

Return the maximum of the “passengers” field from features in the layer grouped by “station_class” field:
```
maximum("passengers", group_by:="station_class")
```
Calculate the total number of passengers for the stations inside the current atlas feature:
```
aggregate('rail_stations','sum',"passengers",
  intersects(@atlas_geometry, $geometry))
```

Return the mean of the “field_from_related_table” field for all matching child features using the ‘my_relation’ relation from the layer:

aggregate_relation('my_relation', 'mean', "field_from_related_table")

aggregate_relation(relation:='my_relation', calculation := 'mean',
  expression := "field_from_related_table")

Funciones de Color ¶

This group contains functions for manipulating colors.

Función	Descripción
color_cmyk	Devuelve una representación en forma de cadena de un color en base a sus componentes cian, magenta, amarillo y negro
color_cmyka	Returns a string representation of a color based on its cyan, magenta, yellow, black and alpha (transparency) components
color_hsl	Returns a string representation of a color based on its hue, saturation, and lightness attributes
color_hsla	Devuelve una representación en forma de cadena de un color en base a sus atributos de matiz, saturación, luminosidad y canal alfa (transparencia).
color_hsv	Returns a string representation of a color based on its hue, saturation, and value attributes
color_hsva	Devuelve una representación en forma de cadena de un color en base a sus atributos de matiz, saturación, valor y canal alfa (transparencia)
color_part	Devuelve un componente específico de la cadena de un color, por ejemplo el componente rojo o el alfa
color_rgb	Returns a string representation of a color based on its red, green, and blue components
color_rgba	Returns a string representation of a color based on its red, green, blue, and alpha (transparency) components
más oscuro	Devuelve una cadena de color más oscura (o más clara)
más claro	Devuelve una cadena de color más clara (o más oscura)
project_color	Devuelve un color del esquema de color del proyecto
ramp_color	Devuelve una cadena que representa un color de una rampa de color
set_color_part	Sets a specific color component for a color string, eg the red component or alpha component

Funciones de conversión ¶

This group contains functions to convert one data type to another (e.g., string to integer, integer to string).

Función	Descripción
to_date	Convierte una cadena de texto en un objeto fecha
to_datetime	Converts a string into a datetime object
to_int	Convierte una cadena de texto a número entero
to_interval	Converts a string to an interval type (can be used to take days, hours, months, etc. of a date)
to_real	Convierte una cadena de texto en número real
to_string	Convierte un número en cadena.
to_time	Converts a string into a time object

Funciones personalizadas ¶

This group contains functions created by the user. See Editor de Funciones for more details.

Funciones de Fecha y Hora ¶

Este grupo contiene funciones para manipular datos de fecha y hora.

Función	Descripción
edad	Returns as an interval the difference between two dates or datetimes
día	Extracts the day from a date or datetime, or the number of days from an interval
day_of_week	Returns a number corresponding to the day of the week for a specified date or datetime
hora	Extracts the hour from a datetime or time, or the number of hours from an interval
minuto	Extracts the minute from a datetime or time, or the number of minutes from an interval
mes	Extracts the month part from a date or datetime, or the number of months from an interval
now	Returns current date and time
segundo	Extracts the second from a datetime or time, or the number of seconds from an interval
semana	Extrae el número de la semana de una fecha o el número de semanas de un intervalo.
year	Extracts the year part from a date or datetime, or the number of years from an interval

This group also shares several functions with the Funciones de conversión ( to_date, to_time, to_datetime, to_interval) and Funciones de cadena (format_date) groups.

Algún ejemplo:

Get today’s month and year in the “month_number/year” format:
```
format_date(now(),'MM/yyyy')
-- Returns '03/2017'
```

Besides these functions, subtracting dates, datetimes or times using the - (minus) operator will return an interval.

Adding or subtracting an interval to dates, datetimes or times, using the + (plus) and - (minus) operators, will return a datetime.

Get the number of days until QGIS 3.0 release:

to_date('2017-09-29') - to_date(now())
-- Returns <interval: 203 days>

The same with time:

to_datetime('2017-09-29 12:00:00') - to_datetime(now())
-- Returns <interval: 202.49 days>

Get the datetime of 100 days from now:

now() + to_interval('100 days')
-- Returns <datetime: 2017-06-18 01:00:00>

Nota

Storing date and datetime and intervals on fields

The ability to store date, time and datetime values directly on fields may depend on the data source’s provider (e.g., shapefiles accept date format, but not datetime or time format). The following are some suggestions to overcame this limitation.

date, Datetime and time can be stored in text type fields after using the to_format() function.

Intervals can be stored in integer or decimal type fields after using one of the date extraction functions (e.g., day() to get the interval expressed in days)

Campos y Valores ¶

Contains a list of fields from the layer.

Generally, you can use the various fields, values and functions to construct the calculation expression, or you can just type it into the box.

To display the values of a field, you just click on the appropriate field and choose between Load top 10 unique values and Load all unique values. On the right side, the Field Values list opens with the unique values. At the top of the list, a search box helps filtering the values. To add a value to the expression you are writing, double click its name in the list.

Sample values can also be accessed via right-click. Select the field name from the list, then right-click to access a context menu with options to load sample values from the selected field.

Fields name should be double-quoted in the expression. Values or string should be simple-quoted.

Funciones Concordancia aproximada ¶

This group contains functions for fuzzy comparisons between values.

Función	Descripción
hamming_distance	Returns the number of characters at corresponding positions within the input strings where the characters are different
levensheim	Returns the minimum number of character edits (insertions, deletions or substitutions) required to change one string to another. Measure the similarity between two strings
longest_common_substring	Returns the longest common substring between two strings
soundex	Returns the Soundex representation of a string

Funciones Generales ¶

Este grupo contiene funciones generales variadas.

Función	Descripción
eval	Evaluates an expression which is passed in a string. Useful to expand dynamic parameters passed as context variables or fields
layer_property	Returns a property of a layer or a value of its metadata. It can be layer name, crs, geometry type, feature count...
var	Returns the value stored within a specified variable. See variable functions below

Funciones de Geometría ¶

This group contains functions that operate on geometry objects (e.g., length, area).

Función	Descripción
$area	Returns the area size of the current feature
$geometry	Returns the geometry of the current feature (can be used for processing with other functions)
$length	Returns the length of the current line feature
$perimeter	Returns the perimeter of the current polygon feature
$x	Returns the x coordinate of the current feature
$x_at(n)	Returns the x coordinate of the nth node of the current feature’s geometry
$y	Returns the y coordinate of the current feature
$y_at(n)	Returns the y coordinate of the nth node of the current feature’s geometry
angle_at_vertex	Returns the bisector angle (average angle) to the geometry for a specified vertex on a linestring geometry. Angles are in degrees clockwise from north
area	Devuelve el perímetro de un objeto de geometría poligonal. Los cálculos están en el Sistema de Referencia Espacial de esta geometría
azimut	Returns the north-based azimuth as the angle in radians measured clockwise from the vertical on point_a to point_b
contorno	Returns the closure of the combinatorial boundary of the geometry (ie the topological boundary of the geometry).
límites	Returns a geometry which represents the bounding box of an input geometry. Calculations are in the Spatial Reference System of this geometry
bounds_height	Returns the height of the bounding box of a geometry. Calculations are in the Spatial Reference System of this geometry
bounds_width	Devuelve la anchura del recuadro delimitador de una geometría. Los cálculos están en el Sistema de Referencia Espacial de esta geometría
buffer	Returns a geometry that represents all points whose distance from this geometry is less than or equal to distance. Calculations are in the Spatial Reference System of this geometry
centroid	Returns the geometric center of a geometry
closest_point	Returns the point on a geometry that is closest to a second geometry
combinar	Devuelve la combinación de dos geometrías
contains(a,b)	Returns 1 (true) if and only if no points of b lie in the exterior of a, and at least one point of the interior of b lies in the interior of a
convex_hull	Returns the convex hull of a geometry (this represents the minimum convex geometry that encloses all geometries within the set)
cruza	Returns 1 (true) if the supplied geometries have some, but not all, interior points in common
difference(a,b)	Returns a geometry that represents that part of geometry a that does not intersect with geometry b
inconexo	Returns 1 (true) if the geometries do not share any space together
distance	Returns the minimum distance (based on Spatial Reference System) between two geometries in projected units
distance_to_vertex	Returns the distance along the geometry to a specified vertex
end_point	Returns the last node from a geometry
exterior_ring	Returns a line string representing the exterior ring of a polygon geometry, or null if the geometry is not a polygon
extrude(geom,x,y)	Returns an extruded version of the input (Multi-) Curve or (Multi-)Linestring geometry with an extension specified by x and y
geom_from_gml	Returns a geometry created from a GML representation of geometry
geom_from_wkt	Returns a geometry created from a well-known text (WKT) representation
geom_to_wkt	Returns the well-known text (WKT) representation of the geometry without SRID metadata
geometry	Devuelve la geometría de un objeto
geometry_n	Returns the nth geometry from a geometry collection, or null if the input geometry is not a collection
interior_ring_n	Returns the geometry of the nth interior ring from a polygon geometry, or null if the geometry is not a polygon
intersección	Returns a geometry that represents the shared portion of two geometries
intersecta	Tests whether a geometry intersects another. Returns 1 (true) if the geometries spatially intersect (share any portion of space) and 0 if they don’t
intersects_bbox	Tests whether a geometry’s bounding box overlaps another geometry’s bounding box. Returns 1 (true) if the geometries spatially intersect (share any portion of space) their bounding box, or 0 if they don’t
is_closed	Returns true if a line string is closed (start and end points are coincident), false if a line string is not closed, or null if the geometry is not a line string
longitud	Returns length of a line geometry feature (or length of a string)
line_interpolate_angle	Returns the angle parallel to the geometry at a specified distance along a linestring geometry. Angles are in degrees clockwise from north.
line_interpolate_point	Returns the point interpolated by a specified distance along a linestring geometry.
line_locate_point	Returns the distance along a linestring corresponding to the closest position the linestring comes to a specified point geometry.
line_merge	Returns a (Multi-)LineString geometry, where any connected LineStrings from the input geometry have been merged into a single linestring.
m	Returns the m value of a point geometry
make_line	Crea una geometría de línea a partir de una serie de geometrías de puntos
make_point(x,y,z,m)	Returns a point geometry from x and y (and optional z or m) values
make_point_m(x,y,m)	Returns a point geometry from x and y coordinates and m values
make_polygon	Crea una geometría de polígono a partir de un anillo exterior y series opcionales de geometrías interiores de anillo
nodes_to_points	Returns a multipoint geometry consisting of every node in the input geometry
num_geometries	Devuelve el número de geometrías en una colección de geometrías o nulo si la geometría de entrada no es una colección
num_interior_rings	Devuelve el número de anillos interiores de un polígono o una colección de geometrías o nulo si la geometría de entrada no es un polígono o una colección
num_points	Devuelve el número de vértices de una geometría.
num_rings	Devuelve el número de anillos (incluidos los anillos exteriores) de un polígono o una colección de geometrías o nulo si la geometría de entrada no es un polígono o una colección
order_parts	Ordena las partes de una MultiGeometría por los criterios dados
solapa	Comprueba si una geometría solapa con otra. Devuelve 1(verdadero) si las geometrías comparten espacio, son de la misma dimensión, pero no están contenidas en la otra.
perímetro	Devuelve el perímetro de un objeto de geometría poligonal. Los cálculos están en el Sistema de Referencia Espacial de esta geometría.
point_n	Returns a specific node from a geometry
point_on_surface	Returns a point guaranteed to lie on the surface of a geometry
proyecto	Returns a point projected from a start point using a distance and bearing (azimuth) in radians
relate	Prueba o devuelve la representación del Modelo de Intersección 9 Extendido Dimensional (DE-9IM) de la relación entre dos geometrías.
invertir	Reverses the direction of a line string by reversing the order of its vertices
segments_to_lines	Returns a multi line geometry consisting of a line for every segment in the input geometry
shortest_line	Returns the shortest line joining two geometries. The resultant line will start at geometry 1 and end at geometry 2
start_point	Returns the first node from a geometry
sym_difference	Returns a geometry that represents the portions of two geometries that do not intersect
toca	Tests whether a geometry touches another. Returns 1 (true) if the geometries have at least one point in common, but their interiors do not intersect
Transformar	Returns the geometry transformed from the source CRS to the destination CRS
Convertir	Returns a translated version of a geometry. Calculations are in the Spatial Reference System of this geometry
unión	Devuelve una geometría que representa el conjunto unión de los puntos de las geometrías.
entre(a,b)	Tests whether a geometry is within another. Returns 1 (true) if geometry a is completely inside geometry b
x	Returns the x coordinate of a point geometry, or the x coordinate of the centroid for a non-point geometry
x_min	Returns the minimum x coordinate of a geometry. Calculations are in the Spatial Reference System of this geometry
x_max	Returns the maximum x coordinate of a geometry. Calculations are in the Spatial Reference System of this geometry
y	Returns the y coordinate of a point geometry, or the y coordinate of the centroid for a non-point geometry
y_min	Returns the minimum y coordinate of a geometry. Calculations are in the Spatial Reference System of this geometry
y_max	Returns the maximum y coordinate of a geometry. Calculations are in the Spatial Reference System of this geometry
z	Returns the z coordinate of a point geometry

Algún ejemplo:

You can manipulate the current geometry with the variable $geometry to create a buffer or get the point on surface:
```
buffer( $geometry, 10 )
point_on_surface( $geometry )
```
Return the x coordinate of the current feature’s centroid:
```
x( $geometry )
```

Send back a value according to feature’s area:

CASE WHEN $area > 10 000 THEN 'Larger' ELSE 'Smaller' END

Record Functions ¶

Este grupo contiene funciones que operan sobre identificadores de registros.

Función	Descripción
$currentfeature	Devuelve el objeto espacial que está siendo evaluado. Se puede usar con la función ‘attribute’ para evaluar los valores de atributo del objeto actual.
$id	Devuelve el ID del objeto de la fila actual
$map	Returns the id of the current map item if the map is being drawn in a composition, or “canvas” if the map is being drawn within the main QGIS window
$rownum	Returns the number of the current row
$scale	Returns the current scale of the map canvas
atributo	Devuelve el valor del atributo especificado de un objeto
get_feature	Devuelve el primer objeto de una capa que coincide con un valor de atributo dado
uuid	Generates a Universally Unique Identifier (UUID) for each row. Each UUID is 38 characters long.

Algún ejemplo:

Return the first feature in layer “LayerA” whose field “id” has the same value as the field “name” of the current feature (a kind of jointure):
```
get_feature( 'layerA', 'id', attribute( $currentfeature, 'name') )
```

Calculate the area of the joined feature from the previous example:

area( geometry( get_feature( 'layerA', 'id', attribute( $currentfeature, 'name') ) ) )

Funciones de cadena ¶

Este grupo contiene funciones que operan sobre cadenas, por ejemplo reemplazar, convertir a mayúsculas.

Función	Descripción
char	Devuelve el carácter asociado con un código unicode
concat	Concatenates several strings to one
format	Da formato a una cadena usando los argumentos proporcionados.
format_date	Formats a date type or string into a custom string format
format_number	Devuelve un número formateado con el separador local de miles (también trunca el número al número de decimales indicado)
left(string, n)	Returns a substring that contains the n leftmost characters of the string
longitud	Returns length of a string (or length of a line geometry feature)
lower	Convierte una cadena a letras minúsculas.
lpad	Returns a string with supplied width padded using the fill character
regexp_replace	Devuelve una cadena en la que se ha remplazado la expresión regular proporcionada
regexp_substr	Devuelve la parte de una cadena que coincide con una expresión regular proporcionada
remplazar	Returns a string with the supplied string replaced
right(cadena, n)	Devuelve una subcadena que contiene los n caracteres más a la derecha de la cadena.
rpad	Returns a string with supplied width padded using the fill character
strpos	Returns the index of a regular expression in a string
substr	Devuelve una parte de una cadena.
Título	Convierte todas las palabras de una cadena a formato de título (todas las palabras en minúscula con la primera letra en mayúscula)
trim	Elimina todos los espacios en blanco (espacios, tabuladores, etc.) de comienzo y final de una cadena.
upper	Convierte una cadena a letras mayúsculas.
wordwrap	Devuelve una cadena ajustada un número de caracteres máximo/mínimo

Funciones recientes ¶

This group contains recently used functions. Any expression used in the Expression dialog is added to the list, sorted from the more recent to the less one. This helps to quickly retrieve any previous expression.

Variables Functions ¶

This group contains dynamic variables related to the application, the project file and other settings. It means that some functions may not be available according to the context:

from the ^{Select by expression} dialog
desde ^{Calculadora de campos} dialog
desde el diálogo de propiedades de la capa
from the print composer

To use these functions in an expression, they should be preceded by @ character (e.g, @row_number). Are concerned:

Función	Descripción
atlas_feature	Devuelve el objeto del atlas actual (como objeto espacial)
atlas_featureid	Devuelve el ID de objeto del atlas actual.
atlas_featurenumber	Returns the number of pages in composition
atlas_filename	Devuelve el nombre de archivo del atlas actual.
atlas_geometry	Devuelve la geometría de objeto del atlas actual
atlas_pagename	Devuelve el nombre de la página del atlas actual
atlas_totalfeatures	Devuelve el número total de objetos en el atlas.
grid_axis	Devuelve el eje de la anotación de la cuadrícula actual (ej.: ‘x’ para longitud, ‘y’ para latitud).
grid_number	Devuelve el valor de anotación de la cuadrícula actual.
item_id	Returns the composer item user ID (not necessarily unique)
item_uuid	Returns the composer item unique ID
layer_id	Devuelve el ID de la capa actual
layer_name	Devuelve el nombre de la capa actual
layout_dpi	Devulve la resolución de la composición (DPI).
layout_numpages	Returns the number of pages in the composition
layout_pageheight	Returns the composition height in mm
layout_pagewidth	Returns the composition width in mm
map_extent_center	Returns the point feature at the center of the map
map_extent_height	Devuelve la altura actual del mapa
map_extent_width	Devuelve el ancho actual del mapa
map_id	Returns the ID of current map destination. This will be ‘canvas’ for canvas renders, and the item ID for composer map renders
map_rotation	Devuelve la rotación actual del mapa
map_scale	Devuelve la escala actual del mapa
project_filename	Returns the filename of current project
project_folder	Returns the folder for current project
project_path	Returns the full path (including file name) of current project
project_title	Devuelve el Título del proyecto actual.
qgis_os_name	Devuelve el nombre del sistema operativo, ej. ‘Windows’, ‘Linux’ o ‘OSX’.
qgis_platform	Devuelve la plataforma de QGIS, ej. ‘Escritorio’ o ‘Servidor’.
qgis_release_name	Devuelve el nombre de la versión actual de QGIS
qgis_version	Devuelve la versión actual de QGIS como cadena
qgis_version_no	Devuelve la versión actual de QGIS como número
symbol_angle	Devuelve el ángulo del símbolo usado para representar el objeto (solo válido para símbolos de marcador).
symbol_color	Returns the color of the symbol used to render the feature
user_account_name	Devuelve el nombre de la cuenta del sistema operativo del usuario actual.
user_full_name	Devuelve el nombre de usuario del sistema operativo del usuario actual.
row_number	Guarda el número de la fila actual.
Valor	Devuelve el valor actual

Editor de Funciones ¶

With the Function Editor, you are able to define your own Python custom functions in a comfortable way.

La pestaña Editor de funciones

The function editor will create new Python files in .qgis2\python\expressions folder and will auto load all functions defined when starting QGIS. Be aware that new functions are only saved in the expressions folder and not in the project file. If you have a project that uses one of your custom functions you will need to also share the .py file in the expressions folder.

Here’s a short example on how to create your own functions:

@qgsfunction(args="auto", group='Custom')
def myfunc(value1, value2, feature, parent):
    pass

The short example creates a function myfunc that will give you a function with two values. When using the args='auto' function argument the number of function arguments required will be calculated by the number of arguments the function has been defined with in Python (minus 2 - feature, and parent).

This function then can be used with the following expression:

myfunc('test1', 'test2')

Your function will be implemented in the Custom functions group of the Expression tab after using the Run Script button.

Se puede encontrar más información sobre cómo crear código Python en:ref:PyQGIS-Developer-Cookbook.

The function editor is not only limited to working with the field calculator, it can be found whenever you work with expressions.

Outdated version of the documentation. Find the latest one here.

Tabla de contenidos

Expresiones¶

The Expression string builder ¶

Lista de funciones ¶

Operadores ¶

Conditionals ¶

Funciones Matemáticas ¶

Aggregates Functions ¶

Funciones de Color ¶

Funciones de conversión ¶

Funciones personalizadas ¶

Funciones de Fecha y Hora ¶

Campos y Valores ¶

Funciones Concordancia aproximada ¶

Funciones Generales ¶

Funciones de Geometría ¶

Record Functions ¶

Funciones de cadena ¶

Funciones recientes ¶

Variables Functions ¶

Editor de Funciones ¶