Add value to array only if not already in, using bash

Question

As I said the title. I tried this code:

    areasArray=()

    while IFS= read -r line
    do
        areaName="$(awk -F ";" '{print $3}')"
        echo $areaName

        if [[ ! " ${areasArray[@]} " =~ " $areaName " ]]; then
            areasArray+=($areaName)
            echo ${areasArray[*]}
        fi
    done < $reportFile

$reportFile refers to a CSV file that looks like this:

something;something;US
something;something;US
something;something;UK
something;something;FR
something;something;UK
something;something;FR

And the array will looks like this: US US UK FR UK FR. But I want every zone to be added only if it's not already there. So it should looks like this: US UK FR. How can I do that? Thanks.

chepner · Accepted Answer · 2020-02-03 17:13:55Z

7

If you need to perform lookup, use an associative array, not an indexed array. Basically, you'll use the keys of the associate array like a set.

declare -A areasArray

while IFS=";" read _ _ areaName _; do
    if [[ ! -v areasArray[$areaName] ]]; then
        areasArray[$areaName]=
    fi
done < "$reportFile"

Unless there is a specific action you want to take only if the key isn't already present, you can skip the if; areasArray[$areaName]= is idempotent.

answered Feb 3, 2020 at 17:13

chepner

538k77 gold badges594 silver badges746 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

user10313661 Over a year ago

I don't understand what areasArray[$areaName]= is supposed to do... How should I add my areas to my array, then?

chepner Over a year ago

It maps the area just read to an empty string. We aren't interested in the values associated with the keys, just the keys (areas) themselves. You can iterate over the areas later with something like for area in "${!areasArray[@]}"; do ... ;done.

chepner Nov 26, 2024 at 17:46

@EvanCarroll What version of bash are you using? 4.2 (maybe 4.3? I don't recall) is required for -v to work with array indexing. I'm intentionally not storing area names as values in the array, though, only as indices.

Collectives™ on Stack Overflow

Add value to array only if not already in, using bash

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related