Subtract values in one dataframe from another

Question

I have two data frames: (these are shortened versions of them)

A

    Link    VU  U   P
1   DVH1    7   1   37
2   DVH2    7   0   38
3   DVH3    10           


        

Answer 1

A faster way than merge (most likely) is to just make sure the second data.frame is in the same row and column order as the first and subtract them from each other:

z <- names(A)[-1]
cbind(A[1], A[z] - B[match(A$Link, B$Link), z])
#   Link VU U  P
# 1 DVH1  5 1 22
# 2 DVH2  3 0 24
# 3 DVH3 10 1 30

---

Here's some sample data:

A <- structure(list(Link = c("DVH1", "DVH2", "DVH3"), VU = c(7L, 7L, 
10L), U = c(1L, 0L, 1L), P = c(37L, 38L, 35L)), .Names = c("Link", 
"VU", "U", "P"), class = "data.frame", row.names = c("1", "2", "3"))

B <- structure(list(Link = c("DVH1", "DVH3", "DVH2"), P = c(15L, 5L, 
14L), U = c(0L, 0L, 0L), VU = c(2L, 0L, 4L)), .Names = c("Link", 
"P", "U", "VU"), class = "data.frame", row.names = c("1", "3", "2"))