从R中的三个向量创建一个命名列表列表

Question

I'm trying to combine three vectors into a list of lists, with one vector being the indexes for the list.

Given

names<-c("a","b","c","d")
id1<-c(1,1,2,2)
id2<-c(3,4,5,6)

I would like to build a list looking like this:

mylist <- list("a" = list(1,3), "b" = list(1,4), "c" = list(2,5), "d" = list(2,6))

Answer 1

I think you are looking for Map

l <- Map(list, id1, id2) # thanks to @thelatemail for suggested improvement
names(l) <- names
identical(mylist, l)
# TRUE

Answer 2

You can do this using mapply and the c function to concatenate the vectors element-wise. setNames conveniently names the result as the function returns:

ll <- setNames( mapply( c , id1 , id2 , SIMPLIFY = FALSE ) , names )

#$a
#[1] 1 3

#$b
#[1] 1 4

#$c
#[1] 2 5

#$d
#[1] 2 6

or perhaps taking advantage of mapply() 's' USE.NAMES argument you can name the first vector to do this, achieving the same result without setNames :

names(id1) <- names
mapply( c , id1 , id2 , SIMPLIFY = FALSE )