I have a data.frame of the following structure (panel data), with 16 levels of time(quarters) 14 levels of geo (countries) and 20 levels of citizen, each of them repeating accordingly in the dataframe.
time geo citizen X
2008Q1 Belgium Afghanistan 22
2008Q1 Belgium Armenia 10
2008Q1 Belgium Bangladesh 25
2008Q1 Belgium Democratic Republic of the Congo 55
2008Q1 Belgium China (including Hong Kong) 5
2008Q1 Belgium Eritrea 8
I would like to create a new column lets say MOVSUM where it will sum variable X for each level of citizen and geo and time for the previous 4 quarters, so that I would have for each quarter, t, how many X's of each citizen in each geo were available during t-4 to t-1 quarters.
Thanks in advance