在嵌套列表中查找包含子元素的顶级元素

Question

I would like to get a list of top level elements that contain a particular sub-element. Suppose I have a nested list:

v <- list(A=list('a', 'b', 'c'), B=list('c','d','e'), C=list('d'))

I am trying to get the list of all top-level elements that have a particular sub element:

• if I am looking for 'c' I would expect to get ('A', 'B').
• if I am looking for 'd' I would expect to get ('B', 'C')

NOTE: prefer a base-R solution but would be interesting to see others

Answer 1

You can use Filter :

names(Filter(function(x) "c" %in% x,v))
# [1] "A" "B"
names(Filter(function(x) "d" %in% x,v))
# [1] "B" "C"

Or with library purrr :

names(purrr::keep(v, ~"c" %in% .))
# [1] "A" "B"
names(purrr::modify_if(v, ~!"c" %in% ., ~NULL))
# [1] "A" "B"

Answer 2

sapply替代Filter

names(v)[sapply(v, function(x) 'c' %in% x)]