* Preparation
clear all
cd "[working directory]"
import excel "WDI_selected.xlsx", firstrow clear

drop TimeCode
rename (Time CountryName CountryCode) (year country code)
destring GDPpercapitaPPP-Lifeexpectancyatbirthmale, replace force

* Create a new frame
frame create cntry_codes

* Load data into a frame
frame cntry_codes: use "Country_classification", clear

* Create estimates, macros and matrices
mean GDPpercapitaPPP
estimates store e1
local a = 1
scalar a = el(r(table),1,1)
mat A = r(table)

* Access estimates, macros and matrices from another frame
cwf cntry_codes    // change to new frame
estimates dir
di `a'
scalar list a
mat list A
// --> all objects which were created in the default frame are also accessible in the new frame!

* Create new objects
local a = 2
scalar a = 4
mat A = J(3,3,1)

* Access new objects from default frame
cwf default
di `a'
scalar list a
mat list A
// --> again, all objects are accessible
// --> very useful to combine estimates etc. across frames