How to use IF condition before running a inner loop of FORV

[Attaullah Shah]

I am struggling with imposing if condition on a inner loop. Consider the following example where a user can input five dependent variables with names S1 S2 S3 S4 S5 or S1H1 S1H2 S1H3 S1H4 S1H5,

    local LHS : word 1 of `varlist'
    local S = substr("`LHS'",1,1)
    local H = substr("`LHS'",3,1)
    local NF: word count `varlist'


forv s=1/`NF'{
  *IF condition is required here
      forv h=1/`NF'{
            reg `S'`s'`H'`h' `flist'
      }
}

let say that the user inputs the first series of dependent variables i.e. S1 S2 S3 S4 S5, then I just need the higher loop i.e.

 forv s=1/`NF'{

However, if the user inputs the second series i.e., S1H1 S1H2 S1H3 S1H4 S1H5, then I need both the outer and inner loops. i.e.

forv s=1/`NF'{
      forv h=1/`NF'{
            reg `S'`s'`H'`h' `flist'
      }
}

[William Lisowski]

I think something like this will do, making use of the "programmer's if" documented in [P] Stata Programming Reference Manual rather than the "if clause" documented as part of the Stata command syntax.

    local LHS : word 1 of `varlist'
    local S = substr("`LHS'",1,1)
    local H = substr("`LHS'",3,1)
    local NF: word count `varlist'


forv s=1/`NF'{
  if "`H'" != "" {
    forv h=1/`NF'{
      reg `S'`s'`H'`h' `flist'
    }
  }
  else {
    reg `S'`s' `flist'
  }
}