返回到前三个单词

Question

试图找到返回R中前三个单词的方法，我尝试了string_r中的单词函数，但只有当句子中至少有三个单词时，它才返回前三个单词。例如，

sentences <- c("Jane saw a cat", "Jane sat down", "Jane sat", "Jane")

word(sentences, 1, 3)

返回Jane saw a、Jane sat down、NA、NA

我希望它能返回前三个单词，即使这个句子有一两个单词。所以我要找的输出是：

返回Jane saw a、Jane sat down、Jane Sat、Jane

Answer 1

1)字符串计数输入的每个组件中的字数，并使用该或3 (以较少者为准)作为返回的字数。

library(stringr)
word(sentences, end = pmin(str_count(sentences, "\\w+"), 3))
## [1] "Jane saw a"    "Jane sat down" "Jane sat"      "Jane" 

2)字符串解决方案2将一些虚拟词附加到末尾，取前3个单词并修剪掉剩下的任何假人。

sentences %>%
  str_c("@ @ @") %>%
  word(end = 3) %>%
  str_replace(" *@.*", "")
## [1] "Jane saw a"    "Jane sat down" "Jane sat"      "Jane"         

3a) Base (与(1)相同的思想可以被翻译成R基，如下所示：

Word <- function(x, end) do.call("paste", read.table(text = x, fill = TRUE)[1:end])

unname(Vectorize(Word)(sentences, end = pmin(lengths(strsplit(sentences, " ")), 3)))
## [1] "Jane saw a"    "Jane sat down" "Jane sat"      "Jane"       

3b) (与(2)相同的思想可以像这样转化为基R。Word来自(3a)。

sentences |>
  paste("@ @ @") |>
  Word(end = 3) |>
  sub(pattern = " *@.*", replacement = "")
## [1] "Jane saw a"    "Jane sat down" "Jane sat"      "Jane"

更新

(1)简化，旧的(1)现在(2)。(3a)和(3b)现在是R基地对应方。

Answer 2

我们可以分道扬镳

sapply(strsplit(sentences, " "), \(x) paste(head(x, 3), collapse=" "))

-output

[1] "Jane saw a"    "Jane sat down" "Jane sat"      "Jane"       

或者使用正则表达式

trimws( sub("^((\\w+\\s+){1,3}).*", "\\1", sentences))

-output

[1] "Jane saw a" "Jane sat"   "Jane"       "Jane" 

如果我们想使用word，那么它可能需要一个coalesce

library(stringr)
library(purrr)
library(dplyr)
map(3:1,  word, string = sentences, start = 1) %>%
    exec(coalesce, !!!.)
[1] "Jane saw a"    "Jane sat down" "Jane sat"      "Jane"