I would like to copy and paste the value from another feature sharing the same id in QGIS.
The feature to take the value from is always the only one with a value other than NULL per "id". Here what I am trying to achieve:
3
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1A nice question, but may I ask what have you tried by so far? What are your ideas? – Taras Dec 29 '20 at 9:25
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1I've thought of using an expression such as if("cat_f" is NULL, group_by:="id", "cat_f"="cat_f", NULL) But it does not make much sense yet... :) – Md01 Dec 29 '20 at 9:30
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What is the logic QGIS should apply for choosing the feature to take the value from? Is there always only one feature with a value other than NULL per "id"? Please add the answer to your question's body. – bugmenot123 Dec 29 '20 at 11:12
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You can use pyqgis:
lyr = iface.activeLayer() #Click layer in layer tree
fieldlist = ['id','cat_f']
data = [[f[fieldname] for fieldname in fieldlist] for f in lyr.getFeatures()]
#data is now: [[1, 'a'], [1, NULL], [2, 'b'], [2, NULL], [2, NULL], [3, NULL], [3, 'c']]
noNullData = [f for f in data if (f[1] is not None) and (f[1]!=NULL)]
#[[1, 'a'], [2, 'b'], [3, 'c']]
d = {id:data for id, data in noNullData}
#{1: 'a', 2: 'b', 3: 'c'}
fieldindex = lyr.fields().indexFromName(fieldlist[1])
#1
with edit(lyr):
for f in lyr.getFeatures():
if f[fieldlist[0]] in d:
f[fieldlist[1]] = d[f[fieldlist[0]]]
lyr.updateFeature(f)
If you want to use QGIS expressions, use this expression here. In the screenshot below, I used it to create a new field, but you can as well use it to update an existing field:
"id" ||
with_variable (
'mapunique',
array_filter(
array_agg (
map ( "id", "cat_f")
),
@element is not NULL
),
array_to_string (
map_avals (
array_get (
array_foreach (
generate_series (
0,
array_length (@mapunique)-1
),
array_get (
@mapunique,
@element
)
), "id"-1
)
)
)
)
