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

What about this?

library(reshape2)
merge(df, melt(Inc, id="ZIP2"), by.x = c("ZIP1", "eth"), by.y = c("ZIP2", "variable"))
  ZIP1 eth value
1    1   A    56
2    1   B    49
3    2   B    10
4    3   A    43
5    5   C    17