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I want to replace all non-standard characters from fields in a dbf table in QGIS.

From https://stackoverflow.com/questions/20078816/replace-non-ascii-characters-with-a-single-space

I see we can use something like

re.sub(r'[^\x00-\x7F]+','_',  "New_Name" )

But I am not sure how to use this in the the Expression or Function Editor module.

So I have a column called "New_Name" which I want the !@#$%^&*()~`+ etc signs removed and replaced with _

Can RE be used or do we need to specify each value to replace using CASE WHEN or Replace -the solution in RE is better if it can be done in QGIS Field Calculator using the regexp_replace expression?

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  • 3
    have you tried using regexp_replace("field",'\W','_'), might be simpler? (not tried it but worth a go)
    – Steven Kay
    May 24, 2016 at 6:30
  • Didn't know you could - I get "An error occurred while evaluating the calculation string: Invalid regular expression '?': bad repetition syntax" this is using [regexp_replace( "New_Name" ,'\W','_')] @StevenKay
    – GeorgeC
    May 24, 2016 at 6:36
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    It looks as if \W might not be supported in regexp_replace(), but it should work in Python's re.sub() ( And I should have used \W+ )
    – Steven Kay
    May 24, 2016 at 6:41
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    @StevenKay - You're close! You just need a double backslash for \\W so the expression should read regexp_replace( "field", '\\W+', '_' ). Consider posting it as an answer :)
    – Joseph
    May 24, 2016 at 9:28
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    @Joseph thanks. That worked perfectly. Steven why don't you add it in as an answer as mentioned by Joseph :-)
    – GeorgeC
    May 24, 2016 at 10:38

1 Answer 1

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You can use the \W (upper case W) to match any non-alphanumeric characters.

If using regexp_replace() it seems you need to escape the backslash, so it becomes \\W (thanks, Joseph!)

For example

regexp_replace( '=+&hello%%£world','\\W+','_')

returns 

_hello_world

If using the python equivalent function re.sub(), you probably won't need to escape the backslash.

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