first letters of each element

[River Huang]

Dear All, I have this data set:

* Example generated by -dataex-. For more info, type help dataex
clear
input str32 ipc str20 wanted
"H02K21/12 H02K21/24"              "H02K H02K"          
"A61K35/78 A61P39/02"              "A61K A61P"          
"H02J15/00"                        "H02J"               
"C08L23/06 C08K3/34 C08J5/18 C09K" "C08L C08K C08J C09K"
end

For each element of the `ipc' variable, I wish to take the first 4 letters to construct `wanted' variable. Any suggestions? Thanks.

[Ali Atia]

gen wanted2 = strtrim(ustrregexra(ipc,"(.{4})(.*?)( |$)","$1 "))

[River Huang]

Dear Ali, Thanks a lot. It works fine.

[Leonardo Guizzetti]

Ali's method is a slick bit of regex. An alternative, in case you wish to do some downstream processing with each 4-digit code could use split.

split ipc, gen(ipcs)
foreach v of varlist ipcs* {
  qui replace `v' = substr(`v', 1, 4)
}
qui compress ipcs*