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Is it possible to use a grepl argument when referring to a list of values, maybe using the %in% operator? I want to take the data below and if the animal name has "dog" or "cat" in it, I want to return a certain value, say, "keep"; if it doesn't have "dog" or "cat", I want to return "discard".
data <- data.frame(animal = sample(c("cat","dog","bird", 'doggy','kittycat'), 50, replace = T)) Now, if I were just to do this by strictly matching values, say, "cat" and "dog', I could use the following approach:
matches <- c("cat","dog") data$keep <- ifelse(data$animal %in% matches, "Keep", "Discard") But using grep or grepl only refers to the first argument in the list:
data$keep <- ifelse(grepl(matches, data$animal), "Keep","Discard") returns
Warning message: In grepl(matches, data$animal) : argument 'pattern' has length > 1 and only the first element will be used Note, I saw this thread in my search, but this doesn't appear to work: grep using a character vector with multiple patterns
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The grepl() stands for “grep logical”. In R it is a built-in function that searches for matches of a string or string vector. The grepl() method takes a pattern and data and returns TRUE if a string contains the pattern, otherwise FALSE.
The grep and grepl functions use regular expressions or literal values as patterns to conduct pattern matching on a character vector. The grep returns indices of matched items or matched items themselves while grepl returns a logical vector with TRUE to represent a match and FALSE otherwise.
Example 2: Apply grep & grepl with Multiple PatternsWe can also use grep and grepl to check for multiple character patterns in our vector of character strings. We simply need to insert an |-operator between the patterns we want to search for.
You can use an "or" (|) statement inside the regular expression of grepl.
ifelse(grepl("dog|cat", data$animal), "keep", "discard") # [1] "keep" "keep" "discard" "keep" "keep" "keep" "keep" "discard" # [9] "keep" "keep" "keep" "keep" "keep" "keep" "discard" "keep" #[17] "discard" "keep" "keep" "discard" "keep" "keep" "discard" "keep" #[25] "keep" "keep" "keep" "keep" "keep" "keep" "keep" "keep" #[33] "keep" "discard" "keep" "discard" "keep" "discard" "keep" "keep" #[41] "keep" "keep" "keep" "keep" "keep" "keep" "keep" "keep" #[49] "keep" "discard" The regular expression dog|cat tells the regular expression engine to look for either "dog" or "cat", and return the matches for both.
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