javascript array - increment value at given key

Question

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;
    }

You're using an array where you should be using an object.

Robby Cornelissen
– Robby Cornelissen

2016-03-25 02:16:14 +00:00
Commented Mar 25, 2016 at 2:16 — Robby Cornelissen
– Robby Cornelissen, Commented Mar 25, 2016 at 2:16

Robby Cornelissen · Accepted Answer · 2016-03-25 02:32:06Z

2

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;
}, {});

edited Mar 25, 2016 at 2:32

answered Mar 25, 2016 at 2:20

Robby Cornelissen

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2 Comments

Arthur Over a year ago

I am trying to keep it as an array key/value so I can plug the data into chart.js after

Robby Cornelissen Over a year ago

Just map it to an array after you're done with your manipulation. I'll update my answer.

Alex Kapustin · Accepted Answer · 2016-03-25 02:19:45Z

1

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);

answered Mar 25, 2016 at 2:19

Alex Kapustin

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1 Comment

Arthur Over a year ago

I want to start the value at 1 - I am trying to plug in the array to chart.js after. When I use the first snippet, .value, cannot read property 'value' of undefined.

Davuz · Accepted Answer · 2016-03-25 02:20:15Z

0

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.

answered Mar 25, 2016 at 2:20

Davuz

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