I am trying to group census tract level populations into Medical Service Study Areas (MSSA), each of which comprise of a unique, mutually exclusive list of census tracts. I have managed to get the census tract numbers organized by MSSA in a column, separated by commas: data=have Obs ct (char) MSSA_ID (char) 1 1210,1202,1300,1401.... 1.1 2 0701,1101,1501,1504.... 2a 3 0100,0200,7101,1700.... 2b Now I want to efficiently apply this as a format to a data set that contains the population of each census tract: data=census_data census_tract population 1210 4581 1202 5142 0701 7412 1101 6233 .... So that I can get the total population of each MSSA: data=want MSSA_ID total_population 1.1 9723 2a 13645 .... Thanks, D
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