Remove Leading Zeros with QGIS Field Calculator

I'd like to take this attribute value: "MAP_PAR_ID": "0160011000", and populate a new field with "16-11".

This works: concat(substr("MAP_PAR_ID",0,3), '-', substr("MAP_PAR_ID",5,3)) but i need to detect leading zeros and not include them

I've tried numerous variations of CASE ELSE statements but can't even detect leading zeros. Feeble attempt below:

CASE
    WHEN substr("MAP_PAR_ID", 0, 1) = '0' THEN substr("MAP_PAR_ID", 1, 2)
    ELSE  substr("MAP_PAR_ID", 0, 3)

    WHEN substr("MAP_PAR_ID", 5, 1) = '0' THEN substr("MAP_PAR_ID", 6, 2)
    ELSE substr("MAP_PAR_ID",5, 3)
END

Would the python console make things a little easier?

Answer

You can use a regex replace for this:

 regexp_replace('0160011000', '0+([1-9]+)0+([1-9]+)0+', '\\1-\\2')
 regexp_replace("MAP_PAR_ID", '0+([1-9]+)0+([1-9]+)0+', '\\1-\\2')

The regex is broken down like this:

• 0+ - Any number of zeros at the start



• ([1-9]+) - Any number of values between 1 and 9. Capture into group 1


• 0+ - Any number of zeros in the middle


• ([1-9]+) - Any number of values between 1 and 9. Capture into group 2


• 0+ - Any number of zeros at the end

The regex_replace function is defined like this:

regexp_replace(string,regex,after) 

So in the after section we use \\1-\\2 to add the values from group 1 and 2 into our new string.