R：regexpr()如何在模式参数中使用向量

2023年8月2日 230次阅读

我想从一组短文中找到的词典中学习术语的位置.问题在于以下代码的最后几行大致基于
From of list of strings, identify which are human names and which are not

library(tm)

pkd.names.quotes <- c(
  "Mr. Rick Deckard",
  "Do Androids Dream of Electric Sheep",
  "Roy Batty",
  "How much is an electric ostrich?",
  "My schedule for today lists a six-hour self-accusatory depression.",
  "Upon him the contempt of three planets descended.",
  "J.F. Sebastian",
  "Harry Bryant",
  "goat class",
  "Holden, Dave",
  "Leon Kowalski",
  "Dr. Eldon Tyrell"
) 


firstnames <- c("Sebastian", "Dave", "Roy",
                "Harry", "Dave", "Leon",
                "Tyrell")

dict  <- sort(unique(tolower(firstnames)))

corp <- VCorpus(VectorSource(pkd.names.quotes))
#strange but Corpus() gives wrong segment numbers for the matches.

tdm  <-
  TermDocumentMatrix(corp, control = list(tolower = TRUE, dictionary = dict))

inspect(corp)
inspect(tdm)

View(as.matrix(tdm))

data.frame(
  Name      = rownames(tdm)[tdm$i],
  Segment = colnames(tdm)[tdm$j],
  Content = pkd.names.quotes[tdm$j],
  Postion = regexpr(
    pattern = rownames(tdm)[tdm$i],
    text = tolower(pkd.names.quotes[tdm$j])
  )
)

输出带有警告,只有第一行正确.

       Name Segment          Content Postion
1       roy       3        Roy Batty       1
2 sebastian       7   J.F. Sebastian      -1
3     harry       8     Harry Bryant      -1
4      dave      10     Holden, Dave      -1
5      leon      11    Leon Kowalski      -1
6    tyrell      12 Dr. Eldon Tyrell      -1

Warning message:
In regexpr(pattern = rownames(tdm)[tdm$i], text = tolower(pkd.names.quotes[tdm$j])) :
  argument 'pattern' has length > 1 and only the first element will be used

我知道使用pattern = paste(vector,collapse =“|”)的解决方案,但我的矢量可能很长(所有流行的名字).

可以有一个简单的矢量化版本的命令或解决方案,每行接受一个新的模式参数？

最佳答案 您可以使用
mapply向量化regexpr：

mapply is a multivariate version of sapply. mapply applies FUN to the first elements of each … argument, the second elements, the third elements, and so on.

使用

data.frame(
  Name      = rownames(tdm)[tdm$i],
  Segment = colnames(tdm)[tdm$j],
  Content = pkd.names.quotes[tdm$j],
  Postion = mapply(regexpr, rownames(tdm)[tdm$i], tolower(pkd.names.quotes[tdm$j]), fixed=TRUE)
)

结果：

               Name Segment          Content Postion
roy             roy       3        Roy Batty       1
sebastian sebastian       7   J.F. Sebastian       6
harry         harry       8     Harry Bryant       1
dave           dave      10     Holden, Dave       9
leon           leon      11    Leon Kowalski       1
tyrell       tyrell      12 Dr. Eldon Tyrell      11

或者,使用stringr str_locate：

Vectorised over string and pattern

它返回：

For str_locate, an integer matrix. First column gives start postion of match, and second column gives end position.

使用

str_locate(tolower(pkd.names.quotes[tdm$j]), fixed(rownames(tdm)[tdm$i]))[,1]

请注意,如果您需要将字符串与固定(即非正则表达式模式)匹配,则使用fixed().否则,删除fixed()和fixed = TRUE.

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