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

First, could you please put a little more effort into making your question readable. I have no clue as to what is supposed to be code and what is commentary. Secondly, maybe cbind() could work? Again it's really hard to read and understand your question. — Chase Grimm
– Chase Grimm, Commented Jun 27, 2016 at 19:37
How do you expect to merge by id when you're only selecting CATEGORY? — ytk
– ytk, Commented Jun 27, 2016 at 19:40
if you subset MBE to only contain the CATEGORY column, there is no longer any id column to merge on — moman822
– moman822, Commented Jun 27, 2016 at 19:40
ncombined <- merge(x = sample_sort, y = MBE[,c("id","CATEGORY")], by = "id", all.x = TRUE) or merge(x = sample_sort, y = MBE[,c(1,4)], by = "id", all.x = TRUE) — Chase Grimm
– Chase Grimm, Commented Jun 27, 2016 at 19:41
thanks! that worked....i was missing the "id' for subset.... — jalsa
– jalsa, Commented Jun 27, 2016 at 20:05

David · Accepted Answer · 2016-06-27 19:42:35Z

2

Try taking out the columns before merging, eg

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

answered Jun 27, 2016 at 19:42

David

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