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How to create custom functions in QGIS using the function editor?
After having tried to explain in a simple way some Basic rules for writing Python scripts for Processing Toolbox in QGIS, this time we will discover the basic rules for writing custom functions in QGIS using the Function Editor.
Which is the list of functions in QGIS?
Returns the count of missing (NULL) values. Returns the calculated inter quartile range from a field or expression. Returns the aggregate majority of values (most commonly occurring value) from a field or expression. group_by – optional expression to use to group aggregate calculations
How are user defined expressions used in QGIS?
Expressions in QGIS have a lot of power and are used in many core features – selection, calculating field values, styling, labelling etc. QGIS also has support for user-defined expressions. With a little bit of python programming, you can define your own functions that can be used within the expression engine.
What happens if somebody edits the same feature in QGIS?
This version of QGIS does not track if somebody else is editing the same feature at the same time as you are. The last person to save its edits wins. For an optimal and accurate edit of the vector layer geometries, we need to set an appropriate value of snapping tolerance and search radius for features vertices.
How does QGIS allow you to reproject data on the fly?
QGIS allows you to reproject data “on the fly”. What this means is that even if the data itself is in another CRS, QGIS can project it as if it were in a CRS of your choice. To enable “on the fly” projection, click on the CRS Status button in the Status Bar along the bottom of the QGIS window:
How to write custom expression functions in Python?
Go to Edit ‣ Select ‣ Select Features By Expression… or click the Select features using an expression button on the Attributes Toolbar. In the Select by Expression dialog, switch to the Function Editor tab. Here you can write any PyQGIS code that will be executed by the expression engine.
Is there wrong indexation for tab in QGIS?
In Windows with QGIS 2.14.1 in the function editor, when I press “enter” to go to the next line, a wrong indexation is introduced. Specifically a “tab” is put at the beginning instead of the 4 “spaces” that are needed in Python.