I have this data about income for every country from 1800 till 2040 :https://www.gapminder.org/data/ that looks something like this:
country 1800 1801 1802 1803
Albania 667 667 667 667
Algeria 715 716 717 718
Andorra 1200 1200 1200 1200
I want to change to something like this:
country year income
Albania 1800 667
Albania 1801 667
Albania 1802 667
Albania 1803 667
Algeria 1800 715
Algeria 1801 716
Algeria 1802 717
Algeria 1803 718
.....
I have no idea from where to start