say that I have
df1$name <- c('A','B','C','D','E')
df1$val <- c(1, 2, 3, 4, 5)
and
df2$name <- c('A','B')
df2$val <-c(6,7)
I want to calculate df2 - df1 s.t. df3 will be
df3$name <- df2$name
df3$val <- df2$val-df1$val[df1$name==df2$name]
and "match" the names so that
df3$val<-c(6-1,7-2)
would be the output. I tried doing this but I couldn't get the syntax correct, thanks in advance!
We can use a join
library(data.table)
setDT(df2)[df1, val := val - i.val, on = .(name)]
df1 <- data.frame(name = LETTERS[1:5], val = 1:5)
df2 <- data.frame(name = LETTERS[1:2], val = 6:7)
Base R:
### your starting data
df1 <- data.frame(name=c('A','B','C','D','E'), val=c(1, 2, 3, 4, 5))
df2 <- data.frame(name=c('A','B'), val=c('6','7'))
### fix strings-to-integers
df2$val <- as.integer(df2$val) # since we want to subtract
### merge and subtract
out <- merge(df1, df2, by = "name")
out$val <- out$val.y - out$val.x
out
# name val.x val.y val
# 1 A 1 6 5
# 2 B 2 7 5
And as akrun started with, this is a merge/join operation; for good discussion and examples on that, see How to join (merge) data frames (inner, outer, left, right), https://stackoverflow.com/a/6188334/3358272.
