Concatenating part of string and sorting it using QGIS

Question

I'd like to know how to concatenate part of a string and sort it.

For example, i have a FIELD1 (string) and i should have the numbers of the string separated with ';' in the FIELD2. Only the numbers are repeated in the records. Moreover, i should sort the numbers ascending about their values.

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How do I create an array string, in the field calculator of QGIS, to do this?

Answer 1

You need to create a new custom python expression in the Field Calculator to extract the numbers and sort them the way you want.

You can use the following expression:

from qgis.core import *
from qgis.gui import *
@qgsfunction(args='auto', group='Custom')
def extract_digits(text_field, feature, parent):
 split_text = text_field.split()
 num = [int(text) for text in split_text if text.isdigit()]
 num_sort = sorted(num)
 join_sort = ';'.join(['{}'.format (i,) for i in num_sort])
 return join_sort

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Then call the function from the custom expression, and use the field name that contains the street names:

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Do not forget to select the new field in which the sorted digits will be saved.

The output will be like this:

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Update

Based on your comment, I updated the script to take into consideration a semicolon (;) that comes directly after a number. Please use the following code:

from qgis.core import *
from qgis.gui import *
@qgsfunction(args='auto', group='Custom')
def extract_digits(text_field, feature, parent):
 split_text = text_field.split(';')
 merge_text = ' '.join(split_text)
 split_text = merge_text.split()
 num = [int(text) for text in split_text if text.isdigit()]
 num_sort = sorted(num)
 join_sort = ';'.join(['{}'.format (i,) for i in num_sort])
 return join_sort

• Mark: Thank you very much! I'll try, i'm sure that it will works. If i already have the "FIELD2" with random numbers separated with ';' , how can i sort these, with ascending values, in a new field? Should i use array_sort? thanks..
• ahmadhanb: @Mark in your case use the above code to create custom expression. Then check Update existing field and select FIELD2, from the custom expression select extract_digits("FIELD1"). The numbers will be sorted in ascending order by the code.
• Mark: ahmadhanb the script doesn't work if there is the number before the ';' (for example ...;avenue 105;...). It doesn't return the number 105 in the list. Is it possible?
• ahmadhanb: @Mark Please use the updated code.
• Mark: Ok, Thank you very much!!