r - 根据ngrams的长度逐行子集数据

Question

我有一个数据框，其中包含许多术语(不同大小的 ngram，最多可达 5 克)及其各自的频率:

df = data.frame(term = c("a", "a a", "a a card", "a a card base", "a a card base ne",
                         "a a divorce", "a a divorce lawyer", "be", "be the", "be the one"), 
                freq = c(131, 13, 3, 2, 1, 1, 1, 72, 17, 5))

这给了我们:

                 term freq
1                   a  131
2                 a a   13
3            a a card    3
4       a a card base    2
5    a a card base ne    1
6         a a divorce    1
7  a a divorce lawyer    1
8                  be   72
9              be the   17
10         be the one    5

我想要的是将 unigrams(只有一个词的术语)、bigrams(有两个词的术语)、trigrams、fourgrams 和 fivegrams 分成不同的数据框:

例如，仅包含 unigrams 的“df1”将如下所示:

                 term freq
1                   a  131
2                  be   72

“df2”(二元组):

                 term freq
1                 a a   13
2              be the   17

“df3”(八卦):

                 term freq
1            a a card    3
2         a a divorce    1
3          be the one    5

等等。任何想法？也许是正则表达式？

Answer 1

您可以按空间数拆分，即

split(df, stringr::str_count(df$term, '\\s+'))

#$`0`
#  term freq
#1    a  131
#8   be   72

#$`1`
#    term freq
#2    a a   13
#9 be the   17

#$`2`
#          term freq
#3     a a card    3
#6  a a divorce    1
#10  be the one    5

#$`3`
#                term freq
#4      a a card base    2
#7 a a divorce lawyer    1

#$`4`
#              term freq
#5 a a card base ne    1

一个完全基于 R 的解决方案(正如@akrun 提到的)，

split(df, lengths(gregexpr("\\S+", df$term)))