New answers tagged expression
0
votes
Moving (snap) lines to nearest features in QGIS
The idea is to snap all the vertices of Layer_A to Layer_B and then create the line_substring() of Layer_B from one to the next of these snapped points. To do so, use the expression below on Layer_A ...
- 67.2k
3
votes
Accepted
Classifying in QGIS into arbitrary number of percentiles instead of quantiles, based on attribute field value
Another answer is to make a custom python function in the advanced field calculator:
from qgis.core import *
from qgis.gui import *
import numpy as np
@qgsfunction(args='auto', group='Custom')
def ...
- 389
4
votes
Classifying in QGIS into arbitrary number of percentiles instead of quantiles, based on attribute field value
You can use the following expression to categorize your field values into any arbitrary number of percentile (n-tiles, so to say), like e.g. into 7 categories: when you have 140 features, the 20 ...
- 67.2k
1
vote
Showing attribute field of date type with years in four digits in QGIS
Explanation:
First, let me clarify the meaning of the code in the brackets (de_CH):
This code refers to Unicode (ICU) Locale Formats, a database that stores local information such as date format, ...
- 389
6
votes
Labeling count points within dissolved buffers in QGIS
This isn't a complete answer but might provide you or others some ideas to combine with other suggestions.
Considerations:
Assumes you are OK with clustering algorithm approach (not necessarily same ...
- 10.8k
1
vote
Accepted
Showing attribute field of date type with years in four digits in QGIS
Under Layer Properties -> Attributes Form
You can select the field and control the Widget that it uses to display that field. In the case of Date fields, this includes controlling the format.
I'm ...
- 3,715
6
votes
Accepted
QGIS Aggregate expression Function with GroupBy argument
Use this expression:
with_variable(
'sedid',
sed_id,
array_sum(
array_agg(
sum_in_kW,
group_by:=group,
filter:=sed_id<=@sedid
)
...
- 67.2k
3
votes
Labeling count points within dissolved buffers in QGIS
If you want indeed to create one label per buffer, it is easier to indeed create dissolved buffers with the box Keep disjoint features separate checked to get one separate feature per "cluster&...
- 67.2k
6
votes
Accepted
Labeling count points within dissolved buffers in QGIS
What is a bit tricky: expressions work on a per-feature basis, so there is no direct way to only label the dissolved buffer (and any indirect way would be too complicated for the task, an overkill). ...
- 67.2k
7
votes
QGIS Aggregate expression Function with GroupBy argument
You can create a virtual layer that will compute this field. You can then export it to a new permanent layer if you wish to persist the result.
Go to the menu Layer > Add Layer > Add/Edit ...
- 40.8k
3
votes
Test whether layer exists using expression in QGIS
If the problem is just the discrepance between @layer_id an the layer's name, you can use operator ~ to perform a regular expression match:
@layer_id ~ 'point'
Or, if it is not just the current layer,...
- 67.2k
3
votes
Accepted
Test whether layer exists using expression in QGIS
You can use function try() together with any other function that uses a layer's name as argument (e.g. overlay_nearest()): if the layer is not found, the function returns an error. try() returns if ...
- 67.2k
3
votes
Test whether layer exists using expression in QGIS
You can use is_layer_visible, it should return false if the layer is not visible or if there is no such layer in the project.
Example:
is_layer_visible('road')
add that as the condition in your CASE ...
- 3,380
3
votes
Test whether layer exists using expression in QGIS
Create an array of all layer names in a project with variable @layers() (all the map layers in the current project as a list) and function layer_property(), then test if a certain layer name (here: '...
- 67.2k
0
votes
QGIS Map Atlas Expression - How to refer to atlas_pagenumber in an expression for elevation symbology
What you want is @atlas_featurenumber. It is accessible whenever the atlas is active.
The @atlas_pagename is the name generated by the Page name expression in the atlas-tab of the print-layout.
Note: ...
- 765
7
votes
Accepted
Is there a way, in QGIS, with an expression, to convert a color to hexadecimal value?
There is no direct function to convert from decimal to hex using QGIS expressions afaik. But using some math, you can create an expression that does the job.
The following expression works for numbers ...
- 67.2k
1
vote
Accepted
Selecting multiple points from an attribute table in QGIS, based on uncategorized field value
Best way to use Select by expression to select, based on an arbitrary array of numbers from the attribute field foto, is to use this expression:
"foto" in (84,46,78,97,18)
You can't ...
- 67.2k
0
votes
Selecting multiple points from an attribute table in QGIS, based on uncategorized field value
If you hace already selected your desired objects, you can use the Extract by expression tool. Simply check the Selected objects checkbox and put a 1 in the Expression box.
- 3,180
6
votes
Capturing all matches (occurences) with QGIS regular expressions
Unfortunately there is a bug(?) in regexp_matches() function. It returns only first occurence of provided pattern.
regexp_matches( 'QGIS is the best GIS solution in the universe!', '(s.)')
returns ...
- 219
7
votes
Accepted
Capturing all matches (occurences) with QGIS regular expressions
I believe the global matching flag is not (yet) supported, but there is a workaround.
regexp_replace comes to the rescue as it will replace any occurrence of the pattern. The key trick is that ...
- 40.8k
2
votes
Accepted
Find angle of segment of line geometry nearest to point
If you specifically do not want to use line_locate_point and line_interpolate_angle, you can do it like so:
First create an array of the segments as geometries.
The distance from each segment to your ...
- 14.7k
1
vote
Accepted
How to extract polygon attribute based on point location using QGIS expressions
Solved it using the following:
aggregate(
layer:='CDD',
aggregate:='max',
expression:="Value",
filter:=contains($geometry, geometry(get_feature('Site Location', 'fid', 1)))
)
- 609
2
votes
Formatting string with QGIS Expression builder: separate groups of fours digits with hyphens
For splitting inputs with fixed length (here: 12 characters), use this expression ("input_text" is the name of the field containing the string you want to format):
array_to_string (
...
- 67.2k
3
votes
Formatting string with QGIS Expression builder: separate groups of fours digits with hyphens
You are incorrectly using double quotes instead of single quotes for string literals. Please read the QGIS user manual about writing expressions https://docs.qgis.org/3.28/en/docs/user_manual/...
- 1,029
4
votes
Formatting string with QGIS Expression builder: separate groups of fours digits with hyphens
This expression here splits any string you insert in line 3 in groups of 4, connected with hyphen -. In line 3, you can also use a fieldname instead to convert the string in this input field:
...
- 67.2k
0
votes
Accepted
Dynamically filtering feature count in QGIS Atlas, Legend
Use the following expression. Delete your expression from the header, but insert it directly to the legend of the categorised entries if you want to create the number of feautures dynamically in the ...
- 67.2k
3
votes
Accepted
QGIS expressions: creating an array based on integer fields returns 0 for field value NULL
For some reason, a explicit cast to the desired type is needed to avoid the conversion:
array(to_int("no"), to_string("txt"))
I don't know if the implicit cast is being performed ...
- 13.9k
1
vote
Moving substring from end to beginning of string in QGIS Attribute table
Another option: Use regular expressions to look for the space between 1) the weekdays part and 2) the time range part. Then split up the string at this position. Use this expression (see below for ...
- 67.2k
1
vote
QGIS field calcuator expression distance between centroid and point feature of another layer
You need to operate on layer where you will want to have the results. In your case layer 1.
You will use the functions distance, closest_point, get_feature_by_id, array_to_string, overlay_nearest.
...
- 33
1
vote
Moving substring from end to beginning of string in QGIS Attribute table
Solution: Regular expressions
Use twice regexp_matches(), once to get the time range part, the second time to get the weekdays part, then concatenate them (replace timestring with your input fieldname)...
- 67.2k
4
votes
QGIS expressions: creating an array based on integer fields returns 0 for field value NULL
It seem that java and PHP (and maybe other langage as well…) revert to 0 for null integer value as the default behavior in array. QGIS likely do the same.
To bypass this default behavior you have to ...
- 15.3k
4
votes
Accepted
Creating a concatenated field with conditions, changing a numeric field to 4 digits
Simply use lpad() function to change COND field value to 4 digits/characters (using 0 as fill character to the left) and use pipes operator || to concatenate:
ID || lpad (COND,4,0) || CDC1 || CDC2
If ...
- 67.2k
3
votes
Creating a concatenated field with conditions, changing a numeric field to 4 digits
Update your field CONCATENATE via Field Calculator with:
CASE
WHEN length("COND")=1 THEN "ID" || '000'|| "COND" ||"CDC1"|| "CDC2"
WHEN length(...
- 2,862
2
votes
Animating travelled path in QGIS without temporal information and temporal controller
A great possibility to create animations in newer QGIS versions (since 3.26) without any temporal information is using the new „Animation Settings“ option in the symbol widget’s Advanced menu:
To ...
- 67.2k
4
votes
Accepted
Updating filter expression or filter value from one layer to another layer in QGIS
As you mentioned, you want the second layer to be a copy of the first one, with another style, but the same Provider Feature Filter. I don't think you can access fields from another layer there, but ...
- 67.2k
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