fix: common_path was returning wrong result when input is length 1

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: MsCoreUtils
 Title: Core Utils for Mass Spectrometry Data
-Version: 1.17.0
+Version: 1.17.1
 Description: MsCoreUtils defines low-level functions for mass
     spectrometry data and is independent of any high-level data
     structures. These functions include mass spectra processing
@@ -80,4 +80,4 @@ BugReports: https://github.com/RforMassSpectrometry/MsCoreUtils/issues
 URL: https://github.com/RforMassSpectrometry/MsCoreUtils
 biocViews: Infrastructure, Proteomics, MassSpectrometry, Metabolomics
 Roxygen: list(markdown=TRUE)
-RoxygenNote: 7.3.1
+RoxygenNote: 7.3.2

NEWS.md

@@ -1,3 +1,10 @@
+# MsCoreUtils 1.17
+
+## MsCoreUtils 1.17.1
+
+- Fix `common_path()` to not return also the file name if the input parameter
+  contains only identical character strings.
+
 # MsCoreUtils 1.15
 
 ## MsCoreUtils 1.15.7

R/file_utils.R

@@ -2,9 +2,12 @@
 #'
 #' @description
 #'
-#' Find the common part of the path for a provided set of files.
+#' Find the common part of the path up to a provided set of files. Be aware that
+#' the last element (after the last file separator) is treated as a *file*.
+#' Thus, if only directories, without files are submitted, the common path
+#' containing these directories is returned.
 #'
-#' @param x `character` with the file names (including paths).
+#' @param x `character` with the **file names** (including paths).
 #'
 #' @param fsep `character(1)` defining the file separator to be used in
 #'     the returned common path. Defaults to the system platform's file
@@ -42,16 +45,21 @@
 #'
 #' ## No path
 #' common_path(c("a.txt", "b.txt"))
+#'
+#' ## Same path for all
+#' common_path(c("a/a.txt", "a/a.txt"))
 common_path <- function(x, fsep = .Platform$file.sep) {
     if (!length(x))
         return(character())
     sx <- strsplit(x, split = "(\\\\)|/")
-    minl <- min(lengths(sx))
-    cpath <- character()
-    for (i in seq_len(minl)) {
-        uvals <- unique(vapply(sx, `[`, character(1), i = i))
-        if (length(uvals) == 1L)
-            cpath <- c(cpath, uvals)
-    }
-    paste0(cpath, collapse = fsep)
+    minl <- min(lengths(sx)) - 1L
+    if (minl > 0) {
+        cpath <- character()
+        for (i in seq_len(minl)) {
+            uvals <- unique(vapply(sx, `[`, character(1), i = i))
+            if (length(uvals) == 1L)
+                cpath <- c(cpath, uvals)
+        }
+        paste0(cpath, collapse = fsep)
+    } else ""
 }

tests/testthat/test_file_utils.R

@@ -11,4 +11,8 @@ test_that("common_path works", {
     expect_equal(common_path(x), "C:/first/second")
     x <- c("C:\\first\\second\\a.txt", "C:\\first\\second\\third\\b.txt")
     expect_equal(common_path(x), "C:/first/second")
+
+    ## Check if we have a single input.
+    expect_equal(common_path("a/b.txt"), "a")
+    expect_equal(common_path("a/b.txt", "a/b.txt"), "a")
 })