R使用%in%从字符向量中删除停用词

Question

我有一个包含字符串的数据框,我想从中删除停用词.我试图避免使用该tm包,因为它是一个大型数据集,tm似乎运行有点慢.我正在使用tm stopword字典.

library(plyr)
library(tm)

stopWords <- stopwords("en")
class(stopWords)

df1 <- data.frame(id = seq(1,5,1), string1 = NA)
head(df1)
df1$string1[1] <- "This string is a string."
df1$string1[2] <- "This string is a slightly longer string."
df1$string1[3] <- "This string is an even longer string."
df1$string1[4] <- "This string is a slightly shorter string."
df1$string1[5] <- "This string is the longest string of all the other strings."

head(df1)
df1$string1 <- tolower(df1$string1)
str1 <-  strsplit(df1$string1[5], " ")

> !(str1 %in% stopWords)
[1] TRUE

这不是我正在寻找的答案.我试图得到一个向量或字符串不在stopWords向量中.

我究竟做错了什么？

Answer 1

您没有正确访问列表,并且您没有从结果中获取元素%in%(它给出了逻辑向量为TRUE/FALSE).你应该做这样的事情:

unlist(str1)[!(unlist(str1) %in% stopWords)]

(要么)

str1[[1]][!(str1[[1]] %in% stopWords)]

对于整个data.framedf1,您可以执行以下操作:

'%nin%' <- Negate('%in%')
lapply(df1[,2], function(x) {
    t <- unlist(strsplit(x, " "))
    t[t %nin% stopWords]
})

# [[1]]
# [1] "string"  "string."
# 
# [[2]]
# [1] "string"   "slightly" "string." 
# 
# [[3]]
# [1] "string"  "string."
# 
# [[4]]
# [1] "string"   "slightly" "shorter"  "string." 
# 
# [[5]]
# [1] "string"   "string"   "strings."

Answer 2

第一的。您应该取消列出str1或使用lapplyif str1is vector：

!(unlist(str1) %in% words)
#>  [1]  TRUE  TRUE FALSE FALSE  TRUE  TRUE FALSE FALSE FALSE FALSE  TRUE

第二。复杂的解决方案：

string <- c("This string is a string.",
            "This string is a slightly longer string.",
            "This string is an even longer string.",
            "This string is a slightly shorter string.",
            "This string is the longest string of all the other strings.")
rm_words <- function(string, words) {
    stopifnot(is.character(string), is.character(words))
    spltted <- strsplit(string, " ", fixed = TRUE) # fixed = TRUE for speedup
    vapply(spltted, function(x) paste(x[!tolower(x) %in% words], collapse = " "), character(1))
}
rm_words(string, tm::stopwords("en"))
#> [1] "string string."                  "string slightly longer string."  "string even longer string."     
#> [4] "string slightly shorter string." "string longest string strings."