Copying categorized colors from line object to point object using QGIS?

Question

I have two layers in QGIS one with point geometry and one with line geometry. Both layers have the same value in the "identification_id" column so I want to copy the colors (categorized by the identification_id) from the point layer to the segment layer. If both were point layers (or line layers) I would just simply right click on the layers and copy and paste the style..

The layers contains hundreds of different values for the identification_id so making it by hand would take too long time..

Any suggestion?

Answer 1

One method is to use Python and copy the values, symbol colour and label from the categorisation of the line layer to the point layer. We can store the line symbology attributes in a dictionary and create a new style using the stored values.

You can test the following code, changing the names of the layers and the field name:

from PyQt5.QtGui import QColor
from qgis.core import QgsProject, QgsSymbol, QgsRendererCategory, QgsCategorizedSymbolRenderer
style_dict = {}
layer_1 = QgsProject.instance().mapLayersByName("Point example")[0]
renderer = layer_1.renderer()
if renderer.type() == "categorizedSymbol":
    for cat in renderer.categories():
        style_dict[cat.value()] = (cat.symbol().color(), cat.label())

categories = []
layer_2 = QgsProject.instance().mapLayersByName("Line example")[0]
for classes, (color, label) in style_dict.items():
    symbol = QgsSymbol.defaultSymbol(layer_2.geometryType())
    symbol.setColor(QColor(color))
    category = QgsRendererCategory(classes, symbol, label)
    categories.append(category)

field = 'ID'
renderer = QgsCategorizedSymbolRenderer(field, categories)
layer_2.setRenderer(renderer)
layer_2.triggerRepaint()

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Example:

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Edit:

If you want to also copy the same field name used in the line layer, replace:

field = 'ID'

with:

field = renderer.classAttribute()

Answer 2

One way to solve the problem is by rule based style. This implementation isn't perfect but it get the colors correct, but all gets into the same category.

Add a new rule and name it, then press on ("simple line" or "simple marker") and then the equation symbol next to "Fill" and then edit. I then used excel to write this next part

Case
WHEN identification_id=     6336(<-my unique numbers)    THEN color_rgb(    255 , 0 ,   0   )   
WHEN identification_id=     6667(<-my unique numbers)    THEN color_rgb(    250 ,   0   ,   0   )
(etc. dragged the different parts)
Else color_rgb(1,1,1)
End

Then a formula like this =A2&B2&C2&D2&E2&F2&G2&H2&I2 to get it all into one column and pasted it all into the editor.