Replacing columns names using a data frame in r

Question

I have the matrix

m <- matrix(1:9, nrow = 3, ncol = 3, byrow = TRUE,dimnames = list(c("s1", "s2", "s3"),c("tom", "dick","bob")))

   tom dick bob
s1   1    2   3
s2   4    5   6
s3   7    8   9

#and the data frame

current<-c("tom", "dick","harry","bob")
replacement<-c("x","y","z","b")
df<-data.frame(current,replacement)

  current replacement
1     tom           x
2    dick           y
3   harry           z
4     bob           b

#I need to replace the existing names i.e. df$current with df$replacement if 
#colnames(m) are equal to df$current thereby producing the following matrix


m <- matrix(1:9, nrow = 3, ncol = 3, byrow = TRUE,dimnames = list(c("s1", "s2", "s3"),c("x", "y","b")))

   x y b
s1 1 2 3
s2 4 5 6
s3 7 8 9

Any advice? Should I use an 'if' loop? Thanks.

Answer 1

You can use which to match the colnames from m with the values in df$current. Then, when you have the indices, you can subset the replacement colnames from df$replacement.

colnames(m) = df$replacement[which(df$current %in% colnames(m))]

In the above:

1. %in% tests for TRUE or FALSE for any matches between the objects being compared.
2. which(df$current %in% colnames(m)) identifies the indexes (in this case, the row numbers) of the matched names.
3. df$replacement[...] is the basic way to subset the column df$replacement returning only the rows matched with step 2.