What is the fastest way to delete an element of an array?

Question

Giving this array:

arr=(hello asd asd1 asd22 asd333)

I want to delete the a especific item by its value, for example asd. I did this:

IFS=' '
echo "${arr[@]/asd/}"

But it returns the following:

hello 1 22 333

So I did this function:

function remove_item() {
    local item_search="$1"
    shift
    local arr_tmp=("${@}")

    if [ ${#arr_tmp[@]} -eq 0 ]; then
        return
    fi

    local index=0
    for item in ${arr_tmp[@]}; do
        if [ "$item" = "$item_search" ]; then
            unset arr_tmp[$index]
            break
        fi
        let index++
    done

    echo "${arr_tmp[*]}"
}

arr=(asd asd1 asd22 asd333)

remove_item 'asd' "${arr[@]}"

Prints the desired output:

hello asd1 asd22 asd333

But I have to use it with very long arrays, and I have to call it a lot of times. And its performance sucks.

Do you have any better alternative to do it? Any tip, trick, or advice will be appreciatted.

Answer 1

You could use a loop to iterate over the array and remove the element that matches the specified value:

for i in "${!arr[@]}"; do
  [[ "${arr[i]}" == "asd" ]] && unset arr[i]
done

If you know that the array would have at most one matching element, you could even break out of the loop:

  [[ "${arr[i]}" == "asd" ]] && unset arr[i] && break
                                            |^^^^^^^^|
                                             (this causes the loop to break
                                              as soon as the element is found)

---

As an example:

$ arr=(asd asd1 asd22 asd333)
$ for i in "${!arr[@]}"; do [[ "${arr[i]}" == "asd" ]] && unset arr[i]; done
$ echo "${arr[@]}"
asd1 asd22 asd333

Answer 2

Probably @devnull's answer is fastest. But it might possibly be faster not to use a loop and instead let grep do the work. Its not very pretty though:

$ arr=(hello asd asd1 asd22 asd333)
$ remove="asd"
$ i=$(paste -d: <(printf "%s\n" "${!arr[@]}") <(printf "%s\n" "${arr[@]}") | grep -m1 -w -E "^[[:digit:]]+:${remove}$")
$ unset arr[${i%:*}]
$