Getting those records which don't match a regex pattern

[Mattia Di Segni]

Dear sirs,
I'm using Stata18 for Mac (Intel 64-bit)
I've been able to get a substring from string variables through regex and to report it in a new variable with the following code:

generate match = regexs(2) if regexm(varname, regex_pattern)

It worked very well in returning the substrings and also output that there were 33,214 missing values generated.
Is there any way to retrieve these records?
Thank you in advance for your support and availability

[Andrew Musau]

'Retrieve' is ambiguous, but if you simply want to browse through these observations:

browse varname if missing(match)

To keep them:

keep if missing(match)

[Mattia Di Segni]

Dear Andrew,
I thank you for your suggestions. Is there any mean to store them on a new variable?

[Andrew Musau]

Either

gen wanted1= varname if missing(match)

or use the negation operator with your regex command

generate wanted2 = varname if !regexm(varname, regex_pattern)

See

help operators