Get elements from a combination of bash arrays given a flat index

combiget.sh

#!/usr/bin/env bash
# combiget: get appropriate elements from a combination of arrays given a flat index

combiget() {
    ind="${1:?'No index.'}"
    arrs=("${@:2}")

    for (( i = 0 ; i < ${#arrs[@]} ; i++)); do
        n="$ind"
        for (( j = i + 1 ; j < ${#arrs[@]} ; j++ )); do
            declare -n ref="${arrs[$j]}"
            (( n /= ${#ref[@]} ))
        done
        declare -n ref="${arrs[$i]}"
        export "${arrs[$i]%[sS]}"="${ref[$(( n % ${#ref[@]} ))]}"
    done
}


combicount() {
    arrs=("${@}")

    n="1"
    for (( i = 0 ; i < ${#arrs[@]} ; i++)); do
        declare -n ref="${arrs[$i]}"
        (( n *= ${#ref[@]} ))
    done

    echo "$n"
}

combiset() {
    arrs=("${@}")

    for (( i = 0 ; i < ${#arrs[@]} ; i++)); do
        declare -n ref="${arrs[$i]}"
        mapfile -t vars <<<"${ref}"
        export "${vars[@]}"
    done
}


test_combiget() {
    IDX=25

    val1s=(a b c d e)
    val2s=(1 2 3 4)
    val3s=(x y z)
    val4s=(val5=3$'\n'val6=4 val5=5$'\n'val6=6)
    keys=(val1s val2s val3s val4s)

    combiget "$IDX" "${keys[@]}"
    combicount "${keys[@]}"
    combiset val4

    echo "$val1"
    echo "$val2"
    echo "$val3"
    echo "$val5"
    echo "$val6"
}