I would like to create 3 categories -- US, Non-US, and Non-US Developed -- using the variable country and dev_status.

US: if country == "United States"
Non-US: if country != "United States"
Non-US Developed: if country != "United States" & dev_status == "Developed Market"

Then I would like to produce a graph consisting 3 line plots of total number of firms for each category.


Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input long year str33 country double firms str16 dev_status
1975 "Argentina"       321 "Emerging Market" 
1975 "Australia"      1319 "Developed Market"
1975 "Austria"          76 "Developed Market"
1975 "Belgium"         290 "Developed Market"
1975 "Brazil"          202 "Emerging Market" 
1975 "Canada"          623 "Developed Market"
1975 "Canada"          865 "Developed Market"
1975 "Cyprus"            . "Developed Market"
1975 "Denmark"         248 "Developed Market"
1975 "Finland"           . "Developed Market"
1975 "France"          724 "Developed Market"
1975 "Germany"         471 "Developed Market"
1975 "Hong Kong"       136 "Developed Market"
1975 "Iran"             54 ""                
1975 "Israel"            . "Emerging Market" 
1975 "Italy"           152 "Developed Market"
1975 "Japan"           988 "Developed Market"
1975 "Japan"          1398 "Developed Market"
1975 "Luxembourg"       76 "Developed Market"
1975 "Mexico"          369 "Emerging Market" 
1975 "Netherlands"     242 "Developed Market"
1975 "New Zealand"       . "Developed Market"
1975 "Norway"            . "Developed Market"
1975 "South Africa"    577 "Emerging Market" 
1975 "Spain"           465 "Developed Market"
1975 "Spain"           476 "Developed Market"
1975 "Sweden"          101 "Developed Market"
1975 "Sweden"          101 "Developed Market"
1975 "Switzerland"     104 "Developed Market"
1975 "Thailand"          . "Emerging Market" 
1975 "United Kingdom" 2820 "Developed Market"
1975 "United States"  1147 "Developed Market"
1975 "United States"  1523 "Developed Market"
1976 "Argentina"       308 "Emerging Market" 
1976 "Australia"      1229 "Developed Market"
1976 "Austria"          74 "Developed Market"
1976 "Belgium"         277 "Developed Market"
1976 "Brazil"          202 "Emerging Market" 
1976 "Canada"          548 "Developed Market"
1976 "Canada"          833 "Developed Market"
1976 "Cyprus"            . "Developed Market"
1976 "Denmark"         247 "Developed Market"
1976 "Finland"           . "Developed Market"
1976 "France"          685 "Developed Market"
1976 "Germany"         469 "Developed Market"
1976 "Hong Kong"       134 "Developed Market"
1976 "Iran"             60 ""                
1976 "Israel"            . "Emerging Market" 
1976 "Italy"           154 "Developed Market"
1976 "Japan"           988 "Developed Market"
1976 "Japan"          1401 "Developed Market"
1976 "Luxembourg"       73 "Developed Market"
1976 "Mexico"          410 "Emerging Market" 
1976 "Netherlands"     234 "Developed Market"
1976 "New Zealand"       . "Developed Market"
1976 "Norway"            . "Developed Market"
1976 "South Africa"    545 "Emerging Market" 
1976 "Spain"           489 "Developed Market"
1976 "Spain"           530 "Developed Market"
1976 "Sweden"           98 "Developed Market"
1976 "Sweden"           98 "Developed Market"
1976 "Switzerland"     106 "Developed Market"
1976 "Thailand"          . "Emerging Market" 
1976 "United Kingdom" 2568 "Developed Market"
1976 "United States"  1141 "Developed Market"
1976 "United States"  1539 "Developed Market"
1977 "Argentina"       302 "Emerging Market" 
1977 "Australia"      1185 "Developed Market"
1977 "Austria"          71 "Developed Market"
1977 "Belgium"         253 "Developed Market"
1977 "Brazil"          200 "Emerging Market" 
1977 "Canada"          491 "Developed Market"
1977 "Canada"          813 "Developed Market"
1977 "Cyprus"            . "Developed Market"
1977 "Denmark"         245 "Developed Market"
1977 "Finland"           . "Developed Market"
1977 "France"          674 "Developed Market"
1977 "Germany"         465 "Developed Market"
1977 "Hong Kong"       130 "Developed Market"
1977 "Iran"             84 ""                
1977 "Israel"            . "Emerging Market" 
1977 "Italy"           154 "Developed Market"
1977 "Japan"           993 "Developed Market"
1977 "Japan"          1407 "Developed Market"
1977 "Luxembourg"       73 "Developed Market"
1977 "Mexico"            . "Emerging Market" 
1977 "Netherlands"     231 "Developed Market"
1977 "New Zealand"       . "Developed Market"
1977 "Norway"            . "Developed Market"
1977 "South Africa"    547 "Emerging Market" 
1977 "Spain"             . "Developed Market"
1977 "Spain"           519 "Developed Market"
1977 "Sweden"           96 "Developed Market"
1977 "Sweden"           96 "Developed Market"
1977 "Switzerland"     116 "Developed Market"
1977 "Thailand"          . "Emerging Market" 
1977 "United Kingdom" 2853 "Developed Market"
1977 "United States"  1043 "Developed Market"
1977 "United States"  1539 "Developed Market"
end