如何用 NA 标记丢失的左手搭配答案

【问题标题】：How to flag missing left-hand collocates with NA如何用 NA 标记丢失的左手搭配
【发布时间】：2021-04-10 11:14:22
【问题描述】：

我想计算引理 GO 的搭配，包括其所有形式，例如 go、goes、gone 等：

go <- c("go after it", "here we go", "he went bust", "go get it go", "i 'm gon na go", "she 's going berserk")

引理形式存储在这个向量中：

lemma_GO <- c("go", "goes", "going", "gone", "went", "gon na")

这个向量将它们变成一个交替模式：

pattern_GO <- paste0("\\b(", paste0(lemma_GO, collapse = "|"), ")\\b")

但是，当使用带有str_extract_all 的模式来提取GO 的紧靠左侧的搭配时，提取会遗漏那些GO 是字符串中的第一个单词并且稍后在字符串中再次出现的字符串：

library(stringr)
str_extract_all(go, paste0("'?\\b[a-z']+\\b(?=\\s?", pattern_GO, ")"))
[[1]]
character(0)

[[2]]
[1] "we"

[[3]]
[1] "he"

[[4]]
[1] "it"

[[5]]
[1] "'m" "na"

[[6]]
[1] "'s"

预期的结果是这样的：

[[1]]
[1] NA

[[2]]
[1] "we"

[[3]]
[1] "he"

[[4]]
[1]  NA  "it"

[[5]]
[1] "'m" "na"

[[6]]
[1] "'s"

在没有左手搭配的情况下，如何修改提取也返回NA？

【问题讨论】：

标签： r regex

【解决方案1】：

您可以在字符串的开头或您的消费模式添加替代匹配：

str_extract_all(go, paste0("('?\\b[a-z']+\\b|^)(?=\\s?", pattern_GO, ")"))

请参阅regex demo。

见R demo：

go <- c("go after it", "here we go", "he went bust", "go get it go", "i 'm gon na go", "she 's going berserk")
lemma_GO <- c("go", "goes", "going", "gone", "went", "gon na")
pattern_GO <- paste0("\\b(", paste0(lemma_GO, collapse = "|"), ")\\b")
library(stringr)
str_extract_all(go, paste0("('?\\b[a-z']+\\b|^)(?=\\s?", pattern_GO, ")"))

输出：

[[1]]
[1] ""

[[2]]
[1] "we"

[[3]]
[1] "he"

[[4]]
[1] ""   "it"

[[5]]
[1] "'m" "na"

[[6]]
[1] "'s"


Sukces #stdin #stdout 0.26s 42528KB
[1] "\\b(go|goes|going|gone|went|gon na)\\b"
[[1]]
[1] ""

[[2]]
[1] "we"

[[3]]
[1] "he"

[[4]]
[1] ""   "it"

[[5]]
[1] "'m" "na"

[[6]]
[1] "'s"

如果你愿意，你可以使用

将所有空项变成NA

res <- str_extract_all(go, paste0("('?\\b[a-z']+\\b|^)(?=\\s?", pattern_GO, ")"))
res <- lapply(res, function(x) ifelse(x=="", NA, x))

【讨论】：