Text in common between two variables

[Esteban Jara]

Hello. I need to generate a variable that indicates the length of the text string that two other text variables have in common from position 1, including spaces. For example:

* Example generated by -dataex-. To install: ssc install dataex
clear
input str18 var1 str19 var2 float THIS_IS
"example number 1"   "example number 123"  16
"esto es una prueba" "esto es otra prueba"  8
end

I do not know how to do it. Could someone help me please? Thanks

[Fei Wang]

Esteban, I'll show a clumsy solution as below.

gen var1_len = strlen(var1)
qui sum var1_len
local len = r(max)
gen var2_len = strlen(var2)
local len = min(`len', r(max))
drop var1_len var2_len

gen v1 = cond(substr(var1,1,1)==substr(var2,1,1)&!mi(substr(var1,1,1))&!mi(substr(var2,1,1)), 1, 0)
gen wanted = v1

forvalues i = 2/`len'  {
    gen v2 = cond(substr(var1,`i',1)==substr(var2,`i',1)&!mi(substr(var1,`i',1))&!mi(substr(var2,`i',1)), 1, 0)
    replace v1 = v1*v2
    replace wanted = wanted + v1
    drop v2
}

drop v1

. l

     +---------------------------------------------------+
     |               var1                  var2   wanted |
     |---------------------------------------------------|
  1. |   example number 1    example number 123       16 |
  2. | esto es una prueba   esto es otra prueba        8 |
     +---------------------------------------------------+

[Esteban Jara]

It served me perfectly, and I don't think it was a clumsy solution. Thank you very much!

[Ali Atia]

An alternative solution using regex:

gen newvar1 = "^" + ustrregexra(var1,"\w| ","$0?")
gen wanted = strlen(ustrregexs(0)) if ustrregexm(var2,newvar1)
drop newvar1

[Esteban Jara]

I tried this solution and it didn't work well... :-( But I think a regex approach has a lot of potential. Thank you!

[wanhaiyou]

An alternative solution using regex:

gen newvar1 = "^" + ustrregexra(var1,"\w| ","$0?")
gen wanted = strlen(ustrregexs(0)) if ustrregexm(var2,newvar1)
drop newvar1

The answer is very good!