Find all indices of vector haystack that are equal to vector needles,
taking into account the order of both vectors, and their duplicate values.
match_all() is essentially a much more efficient version of:
lapply(needles, \(i) which(haystack == i))
Like lapply(needles, \(i) which(haystack == i)), NAs are ignored.
match_all() internally calls collapse::fmatch
and collapse::gsplit.
Core of the code is based on a suggestion by Sebastian Kranz
(author of the 'collapse' package).
Usage
match_all(needles, haystack, unlist = TRUE)
Arguments
- needles, haystack
vectors of the same type.
needles cannot contain NA/NaN.
Long vectors are not supported.
- unlist
Boolean,
indicating if the result should be a single unnamed integer vector (TRUE, default),
or a named list of integer vectors (FALSE).
Value
An integer vector, or list of integer vectors.
If a list, each element of the list corresponds to each value of needles.
When needles and/or haystack is empty, or when haystack is fully NA,
match_all() returns an empty integer vector (if unlist = TRUE),
or an empty list (if unlist = FALSE).
Examples
n <- 200
haystack <- sample(letters, n, TRUE)
needles <- sample(letters, n/2, TRUE)
indices1 <- match_all(needles, haystack)
head(indices1)
#> [1] 24 26 43 72 80 121