wyphan
commented
2 years ago If I remember correctly, this is already implemented as part of the Fortran standard library fortran-lang/stdlib
On Sun, Apr 24, 2022, 12:24 Walter Spector @.***> wrote:
Most languages have sorting procedures in their libraries, and some even have them as operators. Various Fortran implementations have had sorting procedures in their libraries for many many years - yet none are called in a standardized way. Another approach might be to use C Interop to call C's qsort. However it is not as user-friendly as simply calling an intrinsic. It also has performance problems due to the lack of inlining of the required comparison procedure.
I'd like to propose two sets of simple intrinsic functions that accept 1D array arguments of intrinsic types (e.g., integers, reals, and character strings - maybe logicals), and either return a sorted version of the input, or an integer permutation vector ("grade"). The latter should have an optional argument for stability. Using the old HPF function names as examples, but minus HPF's funky DIM= argument:
result = GRADE_DOWN (ARG[, STABLE=logical_scalar]) ! returns permutation vector for accessing input in descending order result = GRADE_UP (ARG[, STABLE=logical_scalar]) ! returns permutation vector for accessing input in ascending order
result = SORT_DOWN (ARG) ! returns input in descending order result = SORT_UP (ARG) ! returns input in ascending order
I like having them in functional form for use in expressions. However I could see also adding intrinsic subroutine versions of SORT_[UP|DOWN] for doing in-place sorts. For example:
call SORT_INPLACE_DOWN (ARG) call SORT_INPLACE_UP (ARG)
The GRADE versions are especially useful with sorting arrays of derived types. Once the permutation vector has been obtained, the individual elements can be accessed or permuted as needed:
type(mytype_t), allocatable :: my_array(:), my_sorted_array(:) integer, allocatable :: perm_vector(:) : perm_vector = GRADE_UP (my_array%key_value) my_sorted_array = my_array(perm_vector)
or even:
my_sorted_array = my_array(GRADE_UP (my_array%key_value))
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Most languages have sorting procedures in their libraries, and some even have them as operators. Various Fortran implementations have had sorting procedures in their libraries for many many years - yet none are called in a standardized way. Another approach might be to use C Interop to call C's qsort. However it is not as user-friendly as simply calling an intrinsic. It also has performance problems due to the lack of inlining of the required comparison procedure.
I'd like to propose two sets of simple intrinsic functions that accept 1D array arguments of intrinsic types (e.g., integers, reals, and character strings - maybe logicals), and either return a sorted version of the input, or an integer permutation vector ("grade"). The latter should have an optional argument for stability. Using the old HPF function names as examples, but minus HPF's funky DIM= argument:
result = GRADE_DOWN (ARG[, STABLE=logical_scalar]) ! returns permutation vector for accessing input in descending order result = GRADE_UP (ARG[, STABLE=logical_scalar]) ! returns permutation vector for accessing input in ascending order
result = SORT_DOWN (ARG) ! returns input in descending order result = SORT_UP (ARG) ! returns input in ascending order
I like having them in functional form for use in expressions. However I could see also adding intrinsic subroutine versions of SORT_[UP|DOWN] for doing in-place sorts. For example:
call SORT_INPLACE_DOWN (ARG) call SORT_INPLACE_UP (ARG)
The GRADE versions are especially useful with sorting arrays of derived types. Once the permutation vector has been obtained, the individual elements can be accessed or permuted as needed:
type(mytype_t), allocatable :: my_array(:), my_sorted_array(:) integer, allocatable :: perm_vector(:) : perm_vector = GRADE_UP (my_array%key_value) my_sorted_array = my_array(perm_vector)
or even:
my_sorted_array = my_array(GRADE_UP (my_array%key_value))