R：regexpr（）如何在模式参数中使用向量

Question

我想从一组短文本中的词典中了解术语的位置。问题出在下面代码的最后几行，大致基于

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，只有第一行是正确的。

       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 pattern=paste(vector,collapse="|") 的解决方案，但我的向量可能很长（所有流行名称）。

能否有此命令的简单矢量化版本或每行接受新模式参数的解决方案？

Answer 1

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returns:

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.

R：regexpr（）如何在模式参数中使用向量

R: regexpr() how to use a vector in pattern parameter

r

regex

vector

vectorization

tm