Feature: loadtxt skiprows and max_rows

src/stdlib_io.fypp

@@ -81,7 +81,7 @@ module stdlib_io
 contains
 
   #:for k1, t1 in KINDS_TYPES
-    subroutine  loadtxt_${t1[0]}$${k1}$(filename, d)
+    subroutine  loadtxt_${t1[0]}$${k1}$(filename, d, skiprows, max_rows)
       !! version: experimental
       !!
       !! Loads a 2D array from a text file.
@@ -93,6 +93,10 @@ contains
       character(len=*), intent(in) :: filename
       !! The array 'd' will be automatically allocated with the correct dimensions
       ${t1}$, allocatable, intent(out) :: d(:,:)
+      !! Skip the first `skiprows` lines, default: 0.
+      integer, intent(in), optional :: skiprows
+      !! Read max_rows lines of content after skiprows lines. The default is -1, to read all the lines.
+      integer, intent(in), optional :: max_rows
       !!
       !! Example
       !! -------
@@ -111,7 +115,10 @@ contains
       !!     ...
       !!
       integer :: s
-      integer :: nrow, ncol, i
+      integer :: nrow, ncol, i, skiprows_, max_rows_
+
+      skiprows_ = max(optval(skiprows, 0), 0)
+      max_rows_ = optval(max_rows, -1)
 
       s = open(filename)
 
@@ -122,10 +129,17 @@ contains
       #:endif
 
       ! determine number or rows
-      nrow = number_of_rows(s)
+      nrow = number_of_rows(s) - skiprows_
+      if ( nrow < 0 ) call error_stop("loadtxt: skipping more rows than present.")
+      if ( max_rows_ < 0 .or. max_rows_ > nrow) max_rows_ = nrow
+
+      allocate(d(max_rows_, ncol))
+
+      do i = 1, skiprows_
+        read(s, *)
+      end do
 
-      allocate(d(nrow, ncol))
-      do i = 1, nrow
+      do i = 1, max_rows_
         #:if 'real' in t1
           read(s, "(*"//FMT_REAL_${k1}$(1:len(FMT_REAL_${k1}$)-1)//",1x))") d(i, :)
         #:elif 'complex' in t1

src/tests/io/test_loadtxt.f90

@@ -19,6 +19,7 @@ subroutine collect_loadtxt(testsuite)
             new_unittest("loadtxt_sp_huge", test_loadtxt_sp_huge), &
             new_unittest("loadtxt_sp_tiny", test_loadtxt_sp_tiny), &
             new_unittest("loadtxt_dp", test_loadtxt_dp), &
+            new_unittest("test_loadtxt_dp_max_skip", test_loadtxt_dp_max_skip), &
             new_unittest("loadtxt_dp_huge", test_loadtxt_dp_huge), &
             new_unittest("loadtxt_dp_tiny", test_loadtxt_dp_tiny), &
             new_unittest("loadtxt_complex", test_loadtxt_complex) &
@@ -134,6 +135,29 @@ subroutine test_loadtxt_dp(error)
     end subroutine test_loadtxt_dp
 
 
+    subroutine test_loadtxt_dp_max_skip(error)
+        !> Error handling
+        type(error_type), allocatable, intent(out) :: error
+        real(dp), allocatable :: input(:,:), expected(:,:)
+        integer :: n, m
+
+        allocate(input(10,10))
+
+        do m = 0, 5
+            do n = 1, 11
+                call random_number(input)
+                input = input - 0.5
+                call savetxt('test_dp_max_skip.txt', input)
+                call loadtxt('test_dp_max_skip.txt', expected, skiprows=m, max_rows=n)
+                call check(error, all(input(m+1:min(n+m,10),:) == expected))
+                deallocate(expected)
+                if (allocated(error)) return
+            end do
+        end do
+
+    end subroutine test_loadtxt_dp_max_skip
+
+
     subroutine test_loadtxt_dp_huge(error)
         !> Error handling
         type(error_type), allocatable, intent(out) :: error