Unique on a dataframe with only selected columns

75

I have a dataframe with >100 columns, and I would to find the unique rows, by comparing only two of the columns. I'm hoping this is an easy one, but I can't get it working with unique or duplicated myself.

In the below, I would like to unique only using id and id2:

data.frame(id=c(1,1,3),id2=c(1,1,4),somevalue=c("x","y","z"))

id id2 somevalue
1   1         x
1   1         y
3   4         z

I would like to obtain either:

id id2 somevalue
1   1         x
3   4         z

or:

id id2 somevalue
1   1         y
3   4         z

(I have no preference which of the unique rows is kept)

This question is tagged with r unique

~ Asked on 2012-03-30 14:22:33

The Best Answer is


128

Ok, if it doesn't matter which value in the non-duplicated column you select, this should be pretty easy:

dat <- data.frame(id=c(1,1,3),id2=c(1,1,4),somevalue=c("x","y","z"))
> dat[!duplicated(dat[,c('id','id2')]),]
  id id2 somevalue
1  1   1         x
3  3   4         z

Inside the duplicated call, I'm simply passing only those columns from dat that I don't want duplicates of. This code will automatically always select the first of any ambiguous values. (In this case, x.)

~ Answered on 2012-03-30 14:38:53


26

Here are a couple dplyr options that keep non-duplicate rows based on columns id and id2:

library(dplyr)                                        
df %>% distinct(id, id2, .keep_all = TRUE)
df %>% group_by(id, id2) %>% filter(row_number() == 1)
df %>% group_by(id, id2) %>% slice(1)

~ Answered on 2018-07-17 18:37:25


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