Extract common names in multiple lists

Question

Good morning everyone,

list1 <- c("hola1", "hola2", "hola3")
list2 <- c("hola1", "hola2", "hola4")
list3 <- c("hola2", "hola7", "hola8")
list4 <- c("hola1", "hola7", "hola8")

Answer 1

You can use intersect in combination with combn . intersect looks for common elements and combn will apply it to all 1vs1 combinations of your lists:

l <- list(c("hola1", "hola2", "hola3"),
          c("hola1", "hola2", "hola4"),
          c("hola2", "hola7", "hola8"),
          c("hola1", "hola7", "hola8"))

combn(length(l), 2, FUN=function(i)intersect(l[[i[1]]], l[[i[2]]]),
      simplify=FALSE)
# [[1]]
# [1] "hola1" "hola2"
#[[2]]
#[1] "hola2"
#[[3]]
#[1] "hola1"
#[[4]]
#[1] "hola2"
#[[5]]
#[1] "hola1"
#[[6]]
#[1] "hola7" "hola8"

Answer 2

You are looking for intersect :

> intersect( list1, list2 )
[1] "hola1" "hola2"

Answer 3

First put the character vectors in a list. Then extract common names in all lists with Reduce() and intersect().

    x <- list(c("hola1", "hola2", "hola3"),
              c("hola1", "hola2", "hola4"),
              c("hola2", "hola7", "hola8"),
              c("hola1", "hola7", "hola8"))

    Reduct(intersect, x)