how to plot different variables of different observations

// IMPORT DATA

// The first part just generates data the way I have it,
//such that you know my data structure.
//Skip to "PLOT MY RESULTS"

clear
webuse grunfeld, clear
g ret=invest/1500
bys company (year): g cumul=ret if _n==1
replace cumul=ret + l.cumul if missing(cumul)
gen country = "empty"
keep if company <8
replace country = "FR" if company ==1
replace country = "US" if company ==2
replace country = "DE" if company ==3
replace country = "FR" if company ==4
replace country = "US" if company ==5
replace country = "DE" if company ==6     
replace country = "FR" if company ==7
    

// Generate EMU identifier
gen emu                  = 0
replace emu              = 1  if (country == "AT") | (country == "BE") |  (country == "ES") | (country == "DE") | (country == "CY")| (country == "FI") | (country == "FR") | (country == "IT") | (country == "NL") | (country == "GR") | (country == "SI")

// compute abnormal returns for countries and countrygroups (EMU)
egen mean_country_cum = mean(cumul), by(year country)  // averages for each country
egen mean_euro_cum = mean(cumul), by(year emu)         // emu average based on averaging all emu companies


// PLOT MY RESULTS 
// here begins the interesting part

// Cumulative returns Euro vs. US
// code that displays mean_country_cum(US) vs. mean_euro_cum against time

twoway plot mean_country_cum if company == 1, mean_euro_cum if company == 2