I tagged all my drawing objects with a identifier which includes square brackets. eg [302] [303] [509].

Edit to add further information.

  • Not all objects are tagged with brackets.
  • A few are tagged with just numbers eg 425, 359.
  • A few are tagged Furrow
  • A few are tagged Z
  • a few are tagged I
  • A few are tagged G?
  • A few are tagged multiple ditches
  • There may be a few others sometimes.

Is there a code which could read the [number] from the text field and paste the number (without the brackets) into the numerical field?

Edit - if possible the tags that are already numbers would transfer as they are, while any purely text can be left blank.

If there is such a code, how and where would I input it?

  • Dont name the new field "2". Try "field2" or something.
    – Bera
    Commented Apr 18, 2018 at 10:26

1 Answer 1


A bit ugly, but this should work in the field calculator:

toint( replace(replace("yourfield", ']', ''), '[', '') ) 

This will create an numeric (integer) field with the number between the brackets.

Edit: I believe this expression will work for your tags:

if(regexp_substr( "input", '(\\d+)') <> '', toint(regexp_substr("input", '(\\d+)')), NULL)

This converts :

  • [number] to number,
  • number to number,
  • any text to NULL,
  • NULL to NULL.
  • Any solution will do. I just assumed it might involve Python. I can't even duplicate a field in the field calculator, and have no idea how to use your code. Sorry, and thanks. How do I tell it which attribute to copy and where to paste the amended version? Commented Apr 18, 2018 at 9:21
  • Well, there is a nice tutorial on QGIS website which explains how to use it. You just have to copy the expression I wrote into the "Expression" field, replace yourfield with the name of the text field containing the number with bracket, and choose the result field name in "Output field name".
    – ArMoraer
    Commented Apr 18, 2018 at 9:28
  • I've managed to make a copy of the field (as a text field and with all the numbers) . I relaced yourfield in the code with that field name, but the calculator says that the expression is invalid. The new field is named 1 and I used this code toint( replace(replace("1", ']', ''), '[', '') ) Commented Apr 18, 2018 at 9:29
  • 1
    This could definitively be the issue ;) Could you please add to your question a copy of your objects tags (or a representative part of it if the list is too long)? There is probably a way to deal with the variety of input formats, using a different expression than the one I came up with.
    – ArMoraer
    Commented Apr 18, 2018 at 10:06
  • 1
    I updated my answer. Let me know if there is still any issue.
    – ArMoraer
    Commented Apr 18, 2018 at 12:18

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