从列表的data.frame元素连接一列

Question

I am looking for an idiomatic way to join a column, say named 'x', which exists in every data.frame element of a list. I came up with a solution with two steps by using lapply and Reduce . The second attempt trying to use only Reduce failed. Can I actually use only Reduce with one anonymous function to do this?

#data
xs <- replicate(5, data.frame(x=sample(letters, 10, T), y =runif(10)), simplify = FALSE)
# This works, but may be still unnecessarily long
otmap = lapply(xs, function(df) df$x)
jotm = Reduce(c, otmap)
# This does not count as another solution:
jotm = Reduce(c, lapply(xs, function(df) df$x))

# Try to use only Reduce function. This produces an error
jotr =Reduce(function(a,b){c(a$x,b$x)}, xs)
# Error in a$x : $ operator is invalid for atomic vectors

Answer 1

We can unlist after extracting the 'x' column

unlist(lapply(xs, `[[`, 'x'))
#[1] b y y i z o q w p d f f z b h m c u f s j e i v y b w j n q e w i r h p z q f x a b v z e x l c q f
#Levels: b d i o p q w y z c f h m s u e j n v r x a l