I am trying to complete a foreach loop with a local string. However, I get local not found error. I want to only keep observations that include the following postal codes.
I am following the local example in the Stata help file and my variable postal code is in string format. Where am I going wrong?
Here is the code:
local postal_cleveland "28086 28150 28152 28021 28090 28114 28073 28020 28017 28151 28169 28089 28038 28042 28136"
foreach x in local postal_cleveland {
keep if strpos(postal_code, `x')
}
local not found
r(111);
I don't know which help file you're alluding to, but there are several errors here, and you have been thrown out by the first. The loop should start
foreach x of local postal_cleveland {
The keywords of and in are not interchangeable.
What you typed with in is legal as any list can follow in, but when you get inside the loop Stata can only interpret local as the name of a string variable or scalar, but you have none such: hence the error message.
Another error has not yet bit you, but should be fixed now. When you are looking for a literal string inside a string variable, you must use " " to delimit the string; otherwise as just seen Stata can only guess that you are giving it the name of a string variable or scalar. So, you need
keep if strpos(postal_code, "`x'")
Yet another error has not yet bit you, but should be fixed now. As soon as you go
keep if strpos(postal_code, "28086")
Stata will follow your instructions and so observations with all the other postal codes will disappear. Then Stata will keep on going and on next seeing
keep if strpos(postal_code, "28150")
it again will follow your instructions. But there are no such observations: you dropped them by implication on the previous iteration. So, now you have no data whatsoever and cannot then do anything useful.
You could avoid the loop altogether and just go
keep if strpos(postal_code, "28086") | strpos(postal_code, "28150") | ...
where the ... imply other calls with different codes. That is just my shorthand because I won't type them out here; it is not Stata syntax!
Or you could use a loop and build up to one (and only one) keep statement.
That could be
gen tokeep = 0
foreach x of local postal_cleveland {
replace tokeep = 1 if strpos(postal_code, "`x'")
}
keep if tokeep
which I recommend as better style.
Otherwise put, keep acts instantly: it keeps observations satisfying the criteria specified and thus drops all others.
Detail: string here means string storage or variable type; string as a (display) format by coincidence only implies the same variables.