#!/bin/bash

#-------------------------------------------------------------------------------
# Example 1 for Bash Tips show 20: deleting individual array elements
#-------------------------------------------------------------------------------

#
# Seed the random number generator with a nanosecond number
#
RANDOM=$(date +%N)

echo "Indexed array"
echo "-------------"

#
# Create indexed array and populate with ad ae ... cf
#
declare -a iarr
mapfile -t iarr < <(printf '%s\n' {a..c}{d..f})

#
# Report element count and show the structure
#
echo "Length: ${#iarr[*]}"
declare -p iarr

#
# Unset a random element
#
ind=$((RANDOM % ${#iarr[*]}))
echo "Element $ind to be removed, contents: ${iarr[$ind]}"
unset "iarr[$ind]"

#
# Report on the result of the element removal
#
echo "Length: ${#iarr[*]}"
declare -p iarr

echo
echo "Associative array"
echo "-----------------"

#
# Create associative array. Populate with the indices from the indexed array
# using the array contents as the subscripts.
#
declare -A aarr
for (( i = 0; i <= ${#iarr[*]}; i++ )); do
    # If there's a "hole" in iarr don't create an element
    [[ -v iarr[$i] ]] && aarr[${iarr[$i]}]=$i
done

#
# Report element count and keys
#
echo "Length: ${#aarr[*]}"
echo "Keys: ${!aarr[*]}"

#
# Use a loop to report array contents in sorted order
#
for key in $(echo "${iarr[@]}" | sort); do
    echo "aarr[$key]=${aarr[$key]}"
done

#
# Make another contiguous indexed array of the associative array's keys. We
# don't care about their order
#
declare -a keys
mapfile -t keys < <(printf '%s\n' ${!aarr[*]})

#
# Unset a random element. The indexed array 'keys' contains the keys
# of the associative array so we use the selected one as a subscript. We use
# this array because it doesn't have any "holes". If we'd used 'iarr' we might
# have hit the "hole" we created earlier!
#
k=$((RANDOM % ${#keys[*]}))
echo "Element '${keys[$k]}' to be removed, contents: ${aarr[${keys[$k]}]}"
unset "aarr[${keys[$k]}]"

#
# Report final element count and keys
#
echo "Length: ${#aarr[*]}"
echo "Keys: ${!aarr[*]}"
declare -p aarr

exit