r中的词干函数答案

【问题标题】：Stemming function in rr中的词干函数
【发布时间】：2020-04-07 08:02:19
【问题描述】：

包corpus 提供了一个自定义的词干提取功能。词干函数应该在给定一个词作为输入时，返回词的词干作为输出。

来自Stemming Words，我采用了以下示例，它使用hunspell 字典进行词干提取。

首先我定义了测试这个函数的句子：

sentences<-c("The color blue neutralizes orange yellow reflections.", 
             "Zod stabbed me with blue Kryptonite.", 
             "Because blue is your favourite colour.",
             "Red is wrong, blue is right.",
             "You and I are going to yellowstone.",
             "Van Gogh looked for some yellow at sunset.",
             "You ruined my beautiful green dress.",
             "You do not agree.",
             "There's nothing wrong with green.")

自定义词干提取函数为：

stem_hunspell <- function(term) {
  # look up the term in the dictionary
  stems <- hunspell::hunspell_stem(term)[[1]]

  if (length(stems) == 0) { # if there are no stems, use the original term
    stem <- term
  } else { # if there are multiple stems, use the last one
    stem <- stems[[length(stems)]]
  }

  stem
}

这段代码

sentences=text_tokens(sentences, stemmer = stem_hunspell)

产生：

> sentences
[[1]]
[1] "the"        "color"      "blue"       "neutralize" "orange"     "yellow"    
[7] "reflection" "."         

[[2]]
[1] "zod"        "stabbed"    "me"         "with"       "blue"       "kryptonite"
[7] "."         

[[3]]
[1] "because"   "blue"      "i"         "your"      "favourite" "colour"   
[7] "."        

[[4]]
[1] "re"    "i"     "wrong" ","     "blue"  "i"     "right" "."    

[[5]]
[1] "you"         "and"         "i"           "are"         "go"         
[6] "to"          "yellowstone" "."          

[[6]]
[1] "van"    "gogh"   "look"   "for"    "some"   "yellow" "at"     "sunset" "."     

[[7]]
[1] "you"       "ruin"      "my"        "beautiful" "green"     "dress"    
[7] "."        

[[8]]
[1] "you"   "do"    "not"   "agree" "."    

[[9]]
[1] "there"   "nothing" "wrong"   "with"    "green"   "."

词干后我想对文本应用其他操作，例如删除停用词。无论如何，当我应用tm-function 时：

removeWords(sentences,stopwords)

对于我的句子，我得到以下错误：

Error in UseMethod("removeWords", x) : 
 no applicable method for 'removeWords' applied to an object of class "list"

如果我使用

unlist(sentences)

我没有得到想要的结果，因为我最终得到了 65 个元素的 chr。期望的结果应该是（例如对于第一句话）：

"the color blue neutralize orange yellow reflection."

【问题讨论】：

标签： r text stemming

【解决方案1】：

如果你想从每个sentence 中删除停用词，你可以使用lapply：

library(tm)
lapply(sentences, removeWords, stopwords())

#[[1]]
#[1] ""           "color"      "blue"       "neutralize" "orange"     "yellow"     "reflection" "."         

#[[2]]
#[1] "zod"        "stabbed"    ""           ""           "blue"       "kryptonite" "."  
#...
#...

但是，从您的预期输出来看，您希望将文本粘贴在一起。

lapply(sentences, paste0, collapse = " ")

#[[1]]
#[1] "the color blue neutralize orange yellow reflection ."

#[[2]]
#[1] "zod stabbed me with blue kryptonite ."
#....

【讨论】：

【解决方案2】：

我们可以使用map

library(tm)
library(purrr)
map(sentences, removeWords, stopwords())
#[[1]]
#[1] ""           "color"      "blue"       "neutralize" "orange"     "yellow"     "reflection"
#[8] "."         

#[[2]]
#[1] "zod"        "stabbed"    ""           ""           "blue"       "kryptonite" "."

【讨论】：