循环时将变量存储在列表中

Question

以下列表“ls”包含三个数据框：

unigrams = data.frame(freq = c(3, 3, 5, 4, 3, 41),
                  term = c("a-list", "a-p", "aaa", "aam", "aamir", "aaron"))
bigrams = data.frame(freq = c(13, 1, 1, 2, 1, 4),
                 term = c("a a", "a abode", "a about", "a absolutely", "a accessory", "a acre")) 
trigrams = data.frame(freq = c(1, 1, 1, 1, 1, 1),
                  term = c("a a card", "a a divorce", "a a dreamer", "a a great", "a a guy", "a a hand"))
ls = list(unigrams, bigrams, trigrams)

这给了我们这个：

[[1]]
  freq   term
1    3 a-list
2    3    a-p
3    5    aaa
4    4    aam
5    3  aamir
6   41  aaron

[[2]]
  freq         term
1   13          a a
2    1      a abode
3    1      a about
4    2 a absolutely
5    1  a accessory
6    4       a acre

[[3]]
  freq        term
1    1    a a card
2    1 a a divorce
3    1 a a dreamer
4    1   a a great
5    1     a a guy
6    1    a a hand

我想将每个数据框中的“term”列按单词数分开，创建“word1”、“word2”、“word3”列。像这样：

  freq  word1
1    3 a-list
2    3    a-p
3    5    aaa
4    4    aam
5    3  aamir
6   41  aaron

  freq     word1        word2
1   13         a            a
2    1         a        abode
3    1         a        about
4    2         a   absolutely
5    1         a    accessory
6    4         a         acre

  freq     word1        word2        word3
1    1         a            a         card
2    1         a            a      divorce
3    1         a            a      dreamer
4    1         a            a        great
5    1         a            a          guy
6    1         a            a         hand

我的尝试：

new_ls = list()
for (i in length(ls)) {
    x = ls[[i]]
    # Split each word in column "term":
    x[,paste("word", 1:i, sep = "")] = as.character(lapply(strsplit(as.character(x$term), split=" "), "[", i))
    x = subset(x, select = -term)
    new_ls[[i]] = x
}

不幸的是，最后这个 sn-p 只在最后一个元素中存储了一些错误的结果：

[[1]]
NULL

[[2]]
NULL

[[3]]
  freq   word1   word2   word3
1    1    card    card    card
2    1 divorce divorce divorce
3    1 dreamer dreamer dreamer
4    1   great   great   great
5    1     guy     guy     guy
6    1    hand    hand    hand

我做错了什么？

Answer 1

splitstackshape 库使这项任务变得简单，

library(splitstackshape)
lapply(ls, function(i) cSplit(i, 'term', sep = ' ', direction = 'wide'))