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#' @title Construct a path relative to another
#'
#' @description
#' Constructs a relative path from path \code{from} to path \code{to}.
#' If this is not possible (i.e. different drive letters on windows systems),
#' \code{NA} is returned.
#'
#' @param to [\code{character(1)}]\cr
#' Where the relative path should point to.
#' @param from [\code{character(1)}]\cr
#' From which part to start.
#' Default is \code{\link[base]{getwd}}.
#' @param ignore.case [\code{logical(1)}]\cr
#' Should path comparisons be made case insensitve?
#' Default is \code{TRUE} on Windows systems and \code{FALSE} on other systems.
#' @return [character(1)]: A relative path.
#' @export
getRelativePath = function(to, from = getwd(), ignore.case = isWindows()) {
numberCommonParts = function(p1, p2) {
for (i in seq_len(min(length(p1), length(p2)))) {
if (p1[i] != p2[i])
return(i - 1L)
}
return(if (is.null(i)) 0L else i)
}
from = splitPath(from)
to = splitPath(to)
assertFlag(ignore.case)
if (length(from$drive) != length(to$drive))
return(NA_character_)
if (length(from$drive) > 0L && length(to$drive) > 0L && from$drive != to$drive)
return(NA_character_)
if (ignore.case)
i = numberCommonParts(tolower(from$path), tolower(to$path))
else
i = numberCommonParts(from$path, to$path)
res = c(rep.int("..", length(from$path) - i), tail(to$path, ifelse(i == 0L, Inf, -i)))
if (length(res) == 0L)
res = "."
collapse(res, .Platform$file.sep)
}
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