#!/bin/bash
# arrayPopulate - bash function to populate array variable from arguments,
#   with ability to group any numbers of element by index (row)..
# Inspired by https://lists.gnu.org/archive/html/bug-bash/2025-07/msg00168.html
# (C) 2025 Felix Hauri - felix@f-hauri.ch
# shellcheck disable=SC2059 # This use printf to map array into format strings

# Doing some cosmetic if script is executed (not sourced).
if [[ $0 = "${BASH_SOURCE[0]}" ]]; then
    exec 4>&1
    exec 3> >(sed -ue 's/^[^ U/]/$ &/;s/^/  /;/[Ee]xit/{$!N;$!N;d}'|
		  sed -ue '/() {/,/^  $ }/{ /() {/! s/$ //}')
    exec 2>&3; exec 1>&3
    trap 'exec 1>&4; exec 2>&4; exec 3>&-; wait; exit 0' 0 1 2 3 6 15
    set -v
fi

arrayPopulate() {
    local -i __origin=0  __lines __FieldByRow=1
    local OPTIND OPTARG __opt __tFmt __nl=$'\1'
    while getopts 'f:O:n:' __opt; do case $__opt in
	f ) __FieldByRow=$OPTARG ;;
	O ) __origin=$OPTARG ;;
	n ) __lines=$OPTARG ;;
	* ) local __oid=$((OPTIND-1))
	    __tFmt='Unknown arg: "%s"!\n'
	    __tFmt+='Usage: %s [-O origin] [-n number] [-f field by row]\n'
	    printf "$__tFmt" "${!__oid}" "${FUNCNAME[0]}" >&2
            return 1;;
    esac; done
    shift "$((OPTIND - 1))"
    local -n __target=$1
    shift
    printf -v __tFmt '%*s' $__FieldByRow
    __tFmt=${__tFmt// /%s"${IFS::1}"}
    __tFmt=${__tFmt%"${IFS::1}"}
    local IFS="$__nl"
    printf -v __tFmt "${__tFmt% }$__nl" "$@"
    mapfile -d "$__nl" -O ${__origin} ${__lines+-n} $__lines -t \
	    __target <<<"${__tFmt%"$__nl"}"
    __tFmt="${__tFmt//[!"$__nl"]}"
    [[ $__lines ]] && [[ $__lines -lt ${#__tFmt} ]] && return
    printf -v "__target[${#__tFmt}+__origin-1]" %s \
	   "${__target[${#__tFmt}+__origin-1]%$'\n'}"
}

# Exit here if script is sourced
[[ $0 = "${BASH_SOURCE[0]}" ]] || { true; return 0;}

dumpArray() {
    local _fmt_str; local -n _array=$1
    printf -v _fmt_str ' [%q]=%%s\n' "${!_array[@]}"
    printf "$_fmt_str" "${_array[@]@Q}"
}

printf -v tmpStr '%s %s %s\n' {a..c}{0..2}
mapfile -t T <<<"${tmpStr%$'\n'}"
dumpArray T
printf -v tmpStr '%s %s %s\n' {d..f}{0..2}
mapfile -O 1 -t T <<<"${tmpStr%$'\n'}"
dumpArray T
printf -v tmpStr '%s %s %s\n' {g..i}{0..2}
mapfile -O 2 -n 1 -t T <<<"${tmpStr%$'\n'}"
dumpArray T
printf -v tmpStr '%s %s %s\n' {a..b}{0..2}
mapfile -O $((${#T[@]}-1)) -t T <<<"${tmpStr%$'\n'}"
dumpArray T

unset T
: Strictly as your initial post
arrayPopulate -f 3                   T {a..c}{0..2}
dumpArray T
arrayPopulate -f 3 -O 1              T {d..f}{0..2}
dumpArray T
arrayPopulate -f3  -O2   -n1         T {g..i}{0..2}
dumpArray T
arrayPopulate -f3  -O$((${#T[@]}-1)) T {a..b}{0..2}
dumpArray T

: With fields containing spaces or newlines
arrayPopulate -f 3 -O 1 T Hello\ {people,world,universe}!
dumpArray T
arrayPopulate -f 3 -O 3 T $'Hello,\n  '{people,world,universe}!
dumpArray T

: There are no help, but
arrayPopulate -h

: Then with another row separator than a space
IFS=, arrayPopulate -f 4 U {942..142..-200}{y..A..-8}
dumpArray U

IFS=';' arrayPopulate -f2 V $'Hello,\n  '{dear,people,world,universe}!
dumpArray V