Question

列表l有三个字符串，分别命名为一个，两个和三个。我想将l转换为数据框，我需要一个名为n的其他列。

l <- list(c("a", "b"), c("c", "d", "e"), c("e"))
n <- c("one", "two", "three")

我可以使用循环来完成它，但我确信有更有效的方法可以做到这一点。

out <- NULL
for (i in 1:length(n)){
  step <- rep(n[i], length(l[[i]]))
  out <- c(out, step)}

df <- as.data.frame(unlist(l))
df$n <- out
df

#  unlist(l)     n
#1         a   one
#2         b   one
#3         c   two
#4         d   two
#5         e   two
#6         e three

Answer 1

使用基数R，基本上可以用两行来完成。

l <- list(c("a", "b"), c("c", "d", "e"), c("e"))
n <- c("one", "two", "three")

#Create an appropriately sized vector of names
nameVector <- unlist(mapply(function(x,y){ rep(y, length(x)) }, l, n))

#Create the result
resultDF <- cbind.data.frame(unlist(l), nameVector)


> resultDF
  unlist(l) nameVector
1         a        one
2         b        one
3         c        two
4         d        two
5         e        two
6         e      three

Answer 2

另一个选择是在将列表的每个元素的名称设置为向量后使用stack：

stack(setNames(l, n))

#  values   ind
#1      a   one
#2      b   one
#3      c   two
#4      d   two
#5      e   two
#6      e three

Answer 3

另一个类似的基本R选项：

do.call(rbind, Map(f = expand.grid, l = l, n = n, stringsAsFactors = F))
#   l     n
# 1 a   one
# 2 b   one
# 3 c   two
# 4 d   two
# 5 e   two
# 6 e three

Answer 4

另一个选项是来自melt

的reshape2

library(reshape2)
melt(setNames(l, n))
#  value    L1
#1     a   one
#2     b   one
#3     c   two
#4     d   two
#5     e   two
#6     e three

或base R

data.frame(value = unlist(l), key = rep(n, lengths(l)))
#   value   key
#1     a   one
#2     b   one
#3     c   two
#4     d   two
#5     e   two
#6     e three

将列表转换为R中的数据框，并添加包含子列表名称的列

4 个答案: