Intersection of lists in R

Question

Is there a function that receives a list x and returns a list y such that y[[i]] = intersect(x[[1]][[i]], x[[2]][[i]], ...) ?

If not, is there a R way to code it in a couple of lines?

Evapotranspiration

Answer 1

Does this work?

x <- list(list(1:3,2:4),list(2:3,4:5),list(3:7,4:5))
maxlen <- max(sapply(x,length))
lapply(seq(maxlen),function(i) Reduce(intersect,lapply(x,"[[",i)))

(intersect only takes two arguments so you have to use Reduce as an additional step)

PS I haven't tried this on any hard cases -- e.g. lists of uneven length.

Rhoads

Answer 2

It seems the Reduce can be simply used as follows:

> Reduce(intersect,  list(v1 = c("a","b","c","d"), 
+                         v2 = c("a","b","e"), 
+                         v3 = c("a","f","g"))) 
[1] "a"

Pragmaticism