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javascriptjqueryarrays
Arthur
Arthur

Reputation: 3942

javascript array - increment value at given key

I have a dynamic array and I am trying to increment the value by 1 if the key exists in the array. According to my debug it is incrementing the key and and creating a second key/value pair.

A snippet of my code: 

        for (var i = 0; i < choices.length; i++) {
            console.log(choices[i]);
            if (choices[i].YearTermId == 1) {
                if (!lookup(firstChoice, choices[i].FirstChoiceOptionId)) {
                    firstChoice.push({
                        key: choices[i].FirstChoiceOptionId,
                        value: 1
                    });
                } else {
                    firstChoice[choices[i].FirstChoiceOptionId] = firstChoice[choices[i].FirstChoiceOptionId] + 1;
                }

more if/else..

    function lookup( arr, name ) {
        for(var i = 0, len = arr.length; i < len; i++) {
            if( arr[ i ].key === name )
                return true;
        }
        return false;
    }

Upvotes: 1

Views: 3943

Answers (3)

Robby Cornelissen
Robby Cornelissen

Reputation: 97120

You're using an array where you should be using an object. If you use an object, your code can be rewritten as:

var firstChoice = {};

for (var i = 0; i < choices.length; i++) {
    var firstChoiceOptionId = choices[i].FirstChoiceOptionId;

    if (choices[i].YearTermId == 1) {
        firstChoice[firstChoiceOptionId] = firstChoice[firstChoiceOptionId]
                ? firstChoice[firstChoiceOptionId] + 1
                : 1;

        /* ... */
    }
}

If you need the data as an array afterwards, just map it:

var firstChoiceArray = Object.keys(firstChoice).map(function(key) {
    return {
        key: key,
        value: firstChoice[key]
    };
});

Conversely, if you have an input array and want to convert it to an object for manipulation, reduce it:

var firstChoice = firstChoiceArray.reduce(function(result, current) {
    result[current.key] = current.value;

    return result;
}, {});

Upvotes: 2

Davuz
Davuz

Reputation: 5266

Try with Array.map: Example:

var a = [{key:"ab","value":1},{key:"cd","value":1},{key:"ef","value":1}];
a.map(function(item){if(item.key == this){item.value++}}, "cd");

So, a[1] will have value 2 after that.

Upvotes: 0

Alex Kapustin
Alex Kapustin

Reputation: 2439

I think you should increment value key, like:

firstChoice[choices[i].FirstChoiceOptionId].value ++;

And I would like to rewrite this code to:

var firstChoice = {};
for (var i = 0; i < choices.length; i++) {
    if (choices[i].YearTermId == 1) {
        if (!firstChoice[choices[i].FirstChoiceOptionId]) {
            firstChoice[choices[i].FirstChoiceOptionId] = 0;
        }
        firstChoice[choices[i].FirstChoiceOptionId]++;
    }
}
console.log(firstChoice);

Upvotes: 1

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