Multiple strings with str_detect R

Question

I want to find multiple strings and put it in a variable, however I keep getting errors.

queries <- httpdf %>% filter(str_detect(payload, "create" || "drop" || "select"))
Error: invalid 'x' type in 'x || y'

queries <- httpdf %>% filter(str_detect(payload, "create" | "drop" | "select"))
Error: operations are possible only for numeric, logical or complex types

queries1 <- httpdf %>% filter(str_detect(payload, "create", "drop", "select"))
Error: unused arguments ("drop", "select")

None of these worked. Is there another way to do it with str_detect or should i try something else? I want them to show up as in the same column as well.

I guess you need paste(c('create', 'drop', 'select'), collapse="|") — akrun
– akrun, Commented Mar 12, 2016 at 19:41

fabilous · Accepted Answer · 2018-05-03 20:42:56Z

98

An even simpler way, in my opinion, for your quite short list of strings you want to find can be:

queries <- httpdf %>% filter(str_detect(payload, "create|drop|select"))

As this is actually what

[...] paste(c("create", "drop", "select"),collapse = '|')) [...]

does, as recommended by @penguin before.

For a longer list of strings you want to detect I would first store the single strings into a vector and then use @penguin's approach, e.g.:

strings <- c("string1", "string2", "string3", "string4", "string5", "string6")
queries <- httpdf %>% 
  filter(str_detect(payload, paste(strings, collapse = "|")))

This has the advantage that you can easily use the vector strings later on as well if you want to or have to.

answered May 3, 2018 at 20:42

fabilous

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Comments

Marcus Nunes · Accepted Answer · 2017-09-09 18:00:09Z

47

This is a way to solve this problem:

queries1 <- httpdf %>% 
  filter(str_detect(payload, paste(c("create", "drop", "select"),collapse = '|')))

edited Sep 9, 2017 at 18:00

Marcus Nunes

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answered Jan 19, 2017 at 10:18

penguin

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2 Comments

RxT Over a year ago

With this example I'm getting "creator" (from "the creator is nice") because of "creat", how do I match only the exact word?

user2363777 Over a year ago

Just a heads up that you need to escape reserved regex characters in your strings, for instance replace "." with "\\.", etc.

CramMasbür · Accepted Answer · 2022-09-15 12:58:45Z

I suggest to use loops for such operations. It is much more versatile, IMHO.

An example httpdf table (also to answer the comment of RxT):

httpdf <- tibble(
  payload = c(
    "the createor is nice",
    "try to create something to select",
    "never catch a dropping knife",
    "drop it like it's hot",
    NA,
    "totaly unrelated" ),
  other_optional_columns = 1:6 )

I use sapply to loop over the search query and apply each string as an individual pattern to str_detect. This returns a matrix with one column per search query sting and one line per subject string, which can be collapsed to return a logical vector of your desire.

queries1 <-
  httpdf[ 
    sapply(
      c("create", "drop", "select"),
      str_detect,
      string = httpdf$payload ) %>%
    rowSums( na.rm = TRUE ) != 0, ]

And of course it can be wrapped in a function to use inside a tidyverse filter:

## function
str_detect_mult <-
  function( subject, query ) {
    sapply(
      query,
      str_detect,
      string = subject ) %>%
    rowSums( na.rm = TRUE ) != 0
}
## tidy code
queries1 <- httpdf %>% filter( str_detect_mult( payload, c("create", "drop", "select") ) )

Easily handle word boarders if you want exact word matches (the "\\b" matches a word border and is joined to the start and end of the string):

str_detect_mult_exact <-
  function( subject, query ) {
    sapply(
      query,
      function(.x)
        str_detect(
          subject,
          str_c("\\b",.x,"\\b") ) ) %>%
    rowSums( na.rm = TRUE ) != 0
}

Easily handle multiple matches (e.g. if you want only lines matching exactly one of the strings, i.e. XOR):

str_detect_mult_xor <-
  function( subject, query ) {
    sapply(
      query,
      str_detect,
      string = subject ) %>%
    rowSums( na.rm = TRUE ) == 1
}

Also works in base R:

## function
str_detect_mult <-
  function( subject, query ) {
    rowSums(sapply(
      query,
      grepl,
      x = subject ), na.rm = TRUE ) != 0
}
## tidy code
queries1 <- httpdf[ str_detect_mult( httpdf$payload, c("create", "drop", "select") ), ]

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