How to find common elements from multiple vectors?

Question

Can anyone tell me how to find the common elements from multiple vectors?

a <- c(1,3,5,7,9)
b <- c(3,6,8,9,10)
c <- c(2,3,4,5,7,9)

I want to get the common elements from the above vectors (ex: 3 and 9)

Solution 1

There might be a cleverer way to go about this, but

intersect(intersect(a,b),c)

will do the job.

EDIT: More cleverly, and more conveniently if you have a lot of arguments:

Reduce(intersect, list(a,b,c))

Solution 2

A good answer already, but there are a couple of other ways to do this:

unique(c[c%in%a[a%in%b]])

or,

tst <- c(unique(a),unique(b),unique(c))
tst <- tst[duplicated(tst)]
tst[duplicated(tst)]

You can obviously omit the unique calls if you know that there are no repeated values within a, b or c.

Solution 3

intersect_all <- function(a,b,...){
  all_data <- c(a,b,...)
  require(plyr)
  count_data<- length(list(a,b,...))
  freq_dist <- count(all_data)
  intersect_data <- freq_dist[which(freq_dist$freq==count_data),"x"]
  intersect_data
}


intersect_all(a,b,c)

UPDATE EDIT A simpler code

intersect_all <- function(a,b,...){
  Reduce(intersect, list(a,b,...))
}

intersect_all(a,b,c)

Comments

[Marek]

It's not a good idea to use c as variable name...

[Mostafa90]

why it's a letter like others ?

[Mathias711]

@DimitriPetrenko because you can declare lists with c(1,2...).

[mariotomo]

+1 for reminding us about Reduce and the correct R capitalization!

[Giora Simchoni]

It is worth noting that intersect is for set operations. If you have elements recurring in the vectors, you will lose this info because the vectors are turned into sets prior to intersect. E.g. intersect(c(1,1,2,3), c(1,1,3,4)) would result in c(1,3), and you might have wanted the result c(1,1,3).

[StatsSorceress]

@GioraSimchoni how could you get c(1,1,3), if that is really what you want?

[Montgomery Clift]

@StatsSorceress Suppose you want the "intersection preserving duplicates" of vectors consisting of positive integers, all in a list L. The following code works: N <- max(unlist(L)); LT <- lapply(L, tabulate, nbins = N); v <- do.call(pmin, LT); unlist(sapply(1:N, function(x) rep(x, v[x]))) Another way to do this would use the match function along with negative subscripting to iteratively remove from each of the vectors every element added to the "kernel".

[kcm]

how can i find common elements across different column in a single dataframe the element are numeric i tried the reduce function not outout i tried converting them into factor still no answer but if i try one by such as intersect(df$a,df$b) etc working ..since i have a total of 40 columns it cumbersome to do it ...can you suggest something shorter