Dropping multiple variables ending within a range of numbers

[Hugo Cooke]

Dear Statlist,

I am currently trying to organise data from the LISS dataset. A number of variables including within this dataset are not of use to me and I am looking to drop these. The variable each end in a numeric value from 1 to 500 and I am looking to drop a number of these all at once. I was hoping to achieve this by telling stata to drop variables ending in (for example) *100 to *200.

I have been trying to do this with a loop function and varlist but have not had any luck. Please find dataex example below, I have only including 4 variable but in effect would be looking to drop variable cw15h498 to cw15h500 without manually repeating the drop *498 *499 *500 an so on. Thank you for your help.

Kind Regards,

Hugo

* Example generated by -dataex-. For more info, type help dataex
clear
input double(cw15h497 cw15h498 cw15h499 cw15h500)
4 3 4 4
3 3 3 3
end
label values cw15h497 cw15h497
label def cw15h497 3 "3", modify
label def cw15h497 4 "4", modify
label values cw15h498 cw15h498
label def cw15h498 3 "3", modify
label values cw15h499 cw15h499
label def cw15h499 3 "3", modify
label def cw15h499 4 "4", modify
label values cw15h500 cw15h500
label def cw15h500 3 "3", modify
label def cw15h500 4 "4", modify

[Carlo Lazzaro]

Hugo:

. foreach var of varlist cw15h497-cw15h500 {
  2. drop cw15h*
  3.  }

works for me.

[Andrew Musau]

This will drop variables ending in 400-999 (or in other words, a variable ending in a digit between 4 and 9 followed by 2 digits).

foreach var of varlist*{
    if ustrregexm("`var'", "[4-9][0-9]{2}$"){
        drop `var'
   }
}

[Hugo Cooke]

Dear Carlo and Andrew,

Thank you for your reply and the two different ways of approaching this hurdle.

Starting with your solution Carlo, I have tried this syntax but have been getter the error message "variable cw15h* not found, r(111)". Do you know why this might be the case? After I have run this command I am finding that the entire database is being dropped (bar the one variable not begining with cw15h)

Thank you Andrew as well, with this code I was able to drop all the variable over 500 which I was looking to drop, but is it possible to further define where the first variable ending drops? So for example rather than dropping 400 - 999 you are able to define it as 427-534)?


For a more precise example, the largest range of uninterrupted variables i am looking to drop run from variable name cw15h190 - cw15h287.

[Andrew Musau]

So for example rather than dropping 400 - 999 you are able to define it as 427-534)?

foreach var of varlist *{
    if inrange(`=real(substr("`var'", -3, 3))', 427, 534){
        drop `var'
    }
}

[Hugo Cooke]

Andrew, thanks so much. That does the job!

[Carlo Lazzaro]

Hugo:
I'm too late to the party.
My bad: my previous code should have been:

 foreach var of varlist cw15h497-cw15h500 {
  2. drop  `var'
  3.  }

.

Happy with reading that Andrew's code fixed the issue.

[Nick Cox]

I would loop to collect the names of variables that qualify and then drop them all once the loop is done.