Dear Statalist users,

this may be a trivial question to you, but I am a little bit struggling to do this.

My data are as this example

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input float year str3 iso3 str36 cntry double high float share
2010 "CSK" "W"  682448769         .
2012 "CSK" "W" 1113816002         .
2010 ""    "A"          .   .736144
2012 ""    "A"          .  .7545093
2010 ""    "B"          . .26385596
2012 ""    "B"          .  .2454907
end
What I would like to do is to have for variable high for countries A and B the values of country W multiplied by the share. But I would like to do this only if the value for high is missing.

So I should have something like

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input float year str3 iso3 str36 cntry double high float share
2010 "CSK" "W"  682448769         .
2012 "CSK" "W" 1113816002         .
2010 ""    "A"          502380567   .736144
2012 ""    "A"         840384531,99  .7545093
2010 ""    "B"      180068175     .26385596
2012 ""    "B"          27338243,6  .2454907
end
Any help would be appreciated!
Thank you!!