With one variable, that's easy enough: count if missing(variable-name). If you have several variables, you can put them in a foreach loop. But if you have to do this for arbitrary lists of variables in several files, it may be interesting to package that foreach loop inside a quick command that might handle special display instructions as well.

Here is one suggestion:

// countIfMissing: display the total count of observations, then
// any counts of missing observations for each variable in a list.
capture prog drop countIfMissing
program countIfMissing

version 11
syntax varlist

quietly count
local count=r(N)

// now make things align nicely
local sum=`count'
local tens=1
while `sum'/10>1 {
   local sum=`sum'/10
   local tens=`tens'+1
}
local width=`tens'+int(`tens'/3)
local varct: list sizeof varlist

di ""
di "Observations:"
di %`width'.0fc `count'
di ""
di "Missing:"
foreach varble in `varlist' {
   qui count if missing(`varble')
   local ct=r(N)
   local pct: di %4.2fc 100*`ct'/`count'
   if `pct'>0 {
      di %`width'.0fc `ct' " `varble' (`pct'%)"
   }
   else {
      local varct=`varct'-1
   }
}
if `varct'==0 {
   local offset=`width'+2
   di _column(`offset') "none of `varlist'"
}
di ""

end

For an example of usage, you can try this:

sysuse auto
local myvars "make price foreign"
countIfMissing `myvars'
countIfMissing m*       // (1)
countIfMissing _all     // (2)

As you can see in (1) and (2), the usual varlist conveniences apply here.

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