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I want to have the color of the lines defined by ean xpression. It has to be looked up in a csv-color-table by an Object-Nr

Layer 1 = Line Objects with 'INVENTORY_TYPE_KEY' (= Object-Nr)

Layer 2 = CSV "IO_Color_Table" with a defined 'Color' (=field_2) for each 'Object-Nr' (=field_1)

attribute( 
    get_feature( 
        'IO_Color_Table_12e2ca88_0a50_47ce_97a3_b38d42613dd7', 
         'INVENTORY_TYPE_KEY'  , 
         'field_1' 
    ),
   ' field_2'
)

The expression does not find the corresponding color. I can't figure out why it is not working.

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2
  • Are both Object-Nr fields the same data type? What are the values in your Color column, color names like blue, red, RGB values, HEX? Commented yesterday
  • both Object-Nr. are String /// Color Table CSV : Field_1 = Object Nr. ( e.g. 3A, 3B, 3C, ... ); Field_2 = Color = HTML ( e.g. #FFC000 ) /// Commented yesterday

2 Answers 2

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1

Try aggregate:

I have a line layer roads with the attribute Object-Nr, and a csv table colors with the same Object-Nr column and a column with color names color_name. The expression also works with the hex column.

aggregate(
  layer:='colors', 
  aggregate:='array_agg', 
  expression:="hex_color", 
  filter:="Object-Nr"=attribute(@parent, 'Object-Nr')
         )[0]

enter image description here

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1

Your expression is almost correct, you're literally just one( two) characters away from the solution: delete the last bracket and insert it before the last comma. You need a closing bracket after calling the value inside the field "Object-Nr", see line 6 in the expression below.

Function get_feature() has three (not four as in your case) arguments, whereas attribute() function in this case requires two (not one) argument.

The correct expression looks like this, where CSV_Color_Table corresponds to layer 2 and the Object-Nr as well as Color fieldnames from the corresponding layers as stated in the expression:

attribute (
    get_feature(
        'CSV_Color_Table',
        'Object-Nr_from_Layer_2',
        "Object-Nr_from_Layer_1"
    ),
    'Color_from_Layer_2'
)
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7
  • Thanks @Bera but could you please be more specific about the function get_feature(layer, attribute, value): attribute = what is looked up = 'Object Nr' in the original Layer ? value = field_1 = "Object Nr" = column name in the CSV table with the 'Object Nr' ? 'Color' = the value to return from the CSV table ? Commented 23 hours ago
  • Sorry, don't understand what you mean? I thought you have these values and fields in your layer? Did you test it? Does it work? Commented 23 hours ago
  • @symbol_label || attribute ( get_feature( 'IO_Color_Table_12e2ca88_0a50_47ce_97a3_b38d42613dd7', 'INVENTORY_TYPE_KEY' , 'field_1' ), 'field_2' ) Commented 23 hours ago
  • like in Excel VLOOKUP i have to adress the cell with the value "color" in the coloumn "field 2". the object number is in the field_1 column. The corresponding Object-Number in the layer is in the colum "Inventoriy_type_Key". Commented 23 hours ago
  • 1
    Yes, but you did not respect the syntax with using single quotes ' for text strings vs. double quotes " for fieldnames, see my expression: this is crucial! Without this, it will not work. When replacing 'field_1' in your expression with "field_1" and deleting the space in ' field_2', it should work, right? Correct syntax is important. Commented 7 hours ago

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