Stata if condition within a loop

Question

I am trying to write a loop with a macro variable that will change depending on the iterated value of the loop. See the code below.

I want to loop over ticker values "QLD" and "DDM" and i want the local macro index to equal "QQQ" if the ticker is "QLD" otherwise "DIA."

foreach ticker in "QLD" "DDM"{
    if `ticker'="QLD"{
        local index = "QQQ"
    }
    else{
        local index = "DIA"
    }
    di `index'
}

Although what you are talking about would be called a variable in many languages, in Stata it is customarily called a local macro, and not a local variable. A Stata variable is (only) a variable (meaning, field or column) in the dataset. (Mata is a different story, but, other way round, it has itself no concept of local macros.) — Nick Cox, Oct 15 '20 at 16:00

score 1 · Accepted Answer · answered Oct 15 '20 at 15:51

1

The code you ask for is more nearly

foreach ticker in QLD DDM {
    if "`ticker'" == "QLD" local index = "QQQ"
    else local index = "DIA"
    
    di "`index'"
}

There are two errors in your code and some more code than you need. The errors are omitting quotation marks where needed and using = to test equality.

This choice alone doesn't need a loop:

   local index = cond("`ticker'" == "QLD", "QQQ", "DIA") 
   di "`index'"

In fact as the command above shows, DDM doesn't obviously need to be mentioned at all. (If it does, then your code is wrong for some other reason.)

answered Oct 15 '20 at 15:51

Nick Cox

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Thank you very much that seems to work. I simplified the problem so that you could find the solution quicker so I the DDM actually is necessary. – Nathan Oct 15 '20 at 16:03
If the real problem is different a (good) answer could be different too, but you would have to tell us about that. – Nick Cox Oct 15 '20 at 16:05

Stata if condition within a loop

1 Answers1