R/comsub.R

In pobsteta/theia2r: An R toolbox to find, download and preprocess Sentinel-2 data

#' @title Find the longest common starting substring or directory
#' @description The function search for the longest common prefix between
#'  multiple strings.
#' @param data A vector of strings
#' @param sep A character which is used to separate elements; default ('')
#'  is used to compare single characters; other useful alternatives are
#'  '/' (or '\\\\\\\\' in Windows) to find the longest common directory, or
#'  ' ' to compare words instead of characters.
#' @return A character with the longest common initial substring
#'
#' @author Luigi Ranghetti, phD (2017) \email{ranghetti.l@@irea.cnr.it}
#' @note Modified from a suggestion taken from
#'  [stackoverflow](https://stackoverflow.com/questions/28273716/r-implementation-for-finding-the-longest-common-starting-substrings-in-a-set-of).
#' @export
#' @importFrom methods is
#' @importFrom magrittr '%>%'
#'
#' @examples
#' strings <- c('/home/user/git/sen2r',
#'              '/home/user/git_data/sen2r/ex/vrt/01_translate/')
#'
#' comsub(strings)
#'
#' comsub(strings, sep='/')

comsub <- function(data, sep = "") {
    . <- NULL  # to avoid NOTE on check
    data_spl <- strsplit(data, sep)
    data_spl_maxlength <- max(sapply(strsplit(data, sep), length))
    which_max <- if (length(unique(data)) > 1) {
        lapply(data_spl, `length<-`, data_spl_maxlength) %>% do.call(rbind, .) %>% apply(2, function(i) {
            !length(unique(i)) == 1
        }) %>% which.max() - 1
    } else {
        length(data_spl[[1]]) - 1  # FIXME ok for dir  with '/', but not with ''
    }
    paste(c(data_spl[[1]][seq_len(which_max)], ""), collapse = sep)
}