merge only one or two columns from a different dataframe in R

Question

I have two sets of dataframes. Below are the first five lines for each.

First Data frame Name: sampel_sort
name                             id         supplier   usage
ABC                             10000079    811121     1
DEF                             10000182    541513     4
Supplier C                      10000484    531110     1
Supplier D                      10000523    541320     1
Supplier E                      10000592    524210     1
Supplier F                      10012711    237110     1

Second data frame Name: MBE
  id    State   total   CATEGORY
10000070    MD       5       MBE
10000182    PR       14      MBE
10000484    TX       1       MBE
10000526    MI       3       MBE
10000592    FL       1       MBE
10000680    ID       14      MBE

My actual dataset has lots more columns. I want to combine the two dataframes, but would like to import only the category column. the following merge statement works:

ncombined <- merge(x = sample_sort, y = MBE, by = "id", all.x = TRUE)

But this gives me all the columns from the MBE dataset. I tried the following in different ways (so that only the category column gets imported). But I am not having any luck. I get an error

ncombined <- merge(x = sample_sort, y = MBE[,c("CATEGORY")], by = "id", all.x = TRUE)

Error in fix.by(by.y, y) : 'by' must specify a uniquely valid column

The final result should be as follows:

First Data frame Name: sample_sort
name                             id         supplier   usage  CATEGORY
ABC                             10000079    811121     1       MBE
DEF                             10000182    541513     4       MBE
Supplier C                      10000484    531110     1       MBE
Supplier D                      10000523    541320     1       MBE
Supplier E                      10000592    524210     1       MBE
Supplier F                      10012711    237110     1       NA

Answer 1

Try taking out the columns before merging, eg

ncombined <- merge(x = sample_sort, y = MBE[,c(1:4)], by = "id", all.x = TRUE)