R - Create a new variable where each observation depends on another table and other variables in the data frame

Question

I have the two following tables:

df <- data.frame(eth = c(\"A\",\"B\",\"B\",\"A\",\"C\"),ZIP1 = c(1,1,2,3,5))
Inc <- data.frame(ZIP2 = c(1,2,3,4,5,6,7)         


        

Answer 1

We can use row/column indexing

df$Inc <- Inc[cbind(match(df$ZIP1, Inc$ZIP2), match(df$eth, colnames(Inc)))]

df
#  eth ZIP1 Inc
#1   A    1  56
#2   B    1  49
#3   B    2  10
#4   A    3  43
#5   C    5  17