Feature: loadtxt skiprows and max_rows

doc/specs/stdlib_io.md

@@ -17,14 +17,18 @@ Loads a rank-2 `array` from a text file.
 
 ### Syntax
 
-`call [[stdlib_io(module):loadtxt(interface)]](filename, array)`
+`call [[stdlib_io(module):loadtxt(interface)]](filename, array [, skiprows] [, max_rows])`
 
 ### Arguments
 
 `filename`: Shall be a character expression containing the file name from which to load the rank-2 `array`.
 
 `array`: Shall be an allocatable rank-2 array of type `real`, `complex` or `integer`.
 
+`skiprows` (optional): Skip the first `skiprows` lines. If skipping more rows than present, a 0-sized array will be returned. The default is 0.
+
+`max_rows` (optional): Read `max_rows` lines of content after `skiprows` lines. A negative value results in reading all lines. A value of zero results in no lines to be read. The default value is -1.
+
 ### Return value
 
 Returns an allocated rank-2 `array` with the content of `filename`.
@@ -314,4 +318,4 @@ program demo_fmt_constants
  print FMT_COMPLEX_DP, c64 ! outputs: 1.0000000000000000E+002 0.0000000000000000E+000
 
 end program demo_fmt_constants
-```
+```

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 +93,13 @@ 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. If skipping more rows than present, a 0-sized array will be returned. The default is 0.
+ integer, intent(in), optional :: skiprows
+ !! Read `max_rows` lines of content after `skiprows` lines.
+ !! A negative value results in reading all lines.
+ !! A value of zero results in no lines to be read.
+ !! The default value is -1.
+ integer, intent(in), optional :: max_rows
  !!
  !! Example
  !! -------
@@ -111,21 +118,32 @@ 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)
 
+ ! determine number or rows
+ nrow = number_of_rows(s)
+ skiprows_ = min(skiprows_, nrow)
+ if ( max_rows_ < 0 .or. max_rows_ > (nrow - skiprows_) ) max_rows_ = nrow - skiprows_
+
  ! determine number of columns
- ncol = number_of_columns(s)
+ ncol = 0
+ if ( skiprows_ < nrow ) ncol = number_of_columns(s, skiprows=skiprows_)
  #:if 'complex' in t1
  ncol = ncol / 2
  #:endif
 
- ! determine number or rows
- nrow = number_of_rows(s)
+ allocate(d(max_rows_, ncol))
 
- allocate(d(nrow, ncol))
- do i = 1, nrow
+ do i = 1, skiprows_
+ read(s, *)
+ end do
+
+ 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
@@ -179,17 +197,25 @@ contains
  #:endfor
 
 
- integer function number_of_columns(s)
+ integer function number_of_columns(s, skiprows)
  !! version: experimental
  !!
  !! determine number of columns
  integer,intent(in) :: s
+ integer, intent(in), optional :: skiprows
 
- integer :: ios
+ integer :: ios, skiprows_, i
  character :: c
  logical :: lastblank
 
+ skiprows_ = optval(skiprows, 0)
+
  rewind(s)
+
+ do i = 1, skiprows_
+ read(s, *)
+ end do
+
  number_of_columns = 0
  lastblank = .true.
  do

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("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