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I want to store a list of variables in a macro and then call that macro inside a mi() statement. The original application is for a programme that uses data I cannot bring online for secrecy reasons, and which will include the following statement: 

generate u = cond(mi(`vars'),., runiform(0,1))

The issue being that mi() requires comma separated variable names but vars is delimited by spaces.

I use the auto dataset and mark to illustrate my problem:

sysuse auto
local myvars foreign price
mark missing if mi(`myvars')

In this example, mi() asks for arguments separated by commas, Stata stops and complains that it cannot find a foreignprice variable. Is there a utility function that will insert the commas between the macro elements?

Kenji
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1 Answers1

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A direct answer to the question as set is to use the macro extended function subinstr to change spaces to commas: 

sysuse auto
local myvars foreign price
local myvars : subinstr local myvars " " ",", all 
mark missing if mi(`myvars')

If the aim is to create a marker variable that marks observations with any values missing on specified variables, then there are other alternative ways, most of which don't need any fiddling with separators in a list. This doesn't purport to be a complete set.

A1. 

 regress foreign price 
 gen missing = !e(sample)

A2. 

 egen missing = rowmiss(foreign price) 
 replace missing = missing > 0

A3. 

 local myvars foreign price 
 local myvars : subinstr local myvars " " ",", all 
 gen missing = missing(`myvars')

A4. 

 gen missing = 0 
 quietly foreach v in foreign price { 
     replace missing = 1 if missing(`v') 
 }

A5. 

 mark missing 
 markout missing foreign price 
 replace missing = !missing

EDIT In the edited question there is reference to this within a program: 

 generate u = cond(mi(`vars'),., runiform(0,1))

I wouldn't do that, even with the macro edited to include commas too, although any issue is more one of personal taste. 

 marksample touse 
 markout `vars' 
 generate u = runiform(0,1) if `touse'

It's likely that the indicator variable so produced is needed, or at least useful, somewhere else in the same program.

Nick Cox
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  • Hi. That does the job. I used mark as the example because it was easier to do, but I intend to use it as a condition inside a programme instead of with mark. – Kenji Apr 04 '18 at 13:29
  • Good, but if your real question is different you need to tell us what it is. – Nick Cox Apr 04 '18 at 13:30
  • Edited the question to clarify the intended application. – Kenji Apr 04 '18 at 13:39