Sorry about that.. here are the 2 dput statement for the 2 dataframe I want to compare
structure(list(town = c("Crewe", "Sandbach", "Middleiwch"), area = c("Cheshire",
"Cheshire", "Cheshire"), total_pop = c(100, 400, 120)), row.names = c(NA,
-3L), class = "data.frame")
structure(list(town = c("Crewe", "Sandbach", "Middleiwch"), area = c("Cheshire",
"Cheshire", "Cheshire"), total_pop = c(120, 350, 100)), row.names = c(NA,
-3L), class = "data.frame")
and this the result I want
structure(list(town = c("Crewe", "Sandbach", "Middleiwch"), area = c("Cheshire",
"Cheshire", "Cheshire"), total_pop = c(20, -50, -20)), row.names = c(NA,
-3L), class = "data.frame")]