Javascript - Create and populate associative array containing sub arrays

Question

I'm trying to collate some data. I would like to populate an array containing sub arrays, for example, I have some json data that I am iterating over:

{
    "name": "name1",
    "prices": "209.67"
},
{
    "name": "name1",
    "prices": "350"
},
{
    "name": "name2",
    "price": "195.97"
},

I would like to create an array that ends up looking something like the following:

myArray['name1']prices[0] = 209.67,
               prices[1] = 350,
       ['name2']prices[0] = 195.97

I thought that the code below would achieve what I wanted but it doesn't work. It throws an exception. It doesn't seem to recognise the fact that the prices are an array for a given index into the main array. Instead the prices appear at the same level as the names. I want the main array for a given name to contain an inner array of prices.. Does anybody have any idea how I could modify to make this work?

function doStuff() {
  var cryptoData = getData();

  var datasetValues = {};
  datasetValues.names = [];
  datasetValues.names.prices = [];

  for (var result = 0; result < cryptoData.length; result++) {

    var data = cryptoData[result];

    if (datasetValues.names.indexOf(data.cryptoname) === -1)
    {
      datasetValues.names.push(data.cryptoname);
    }

    // This works
    //datasetValues.names.prices.push(data.prices);

    // This doesn't!
    datasetValues.cryptoNames[data.cryptoname].prices.push(data.prices);
  }
}

Each json result contains a single price but there could be more than one occurrence of a given name as indicated in the json above? — Yos
– Yos, Commented Nov 5, 2018 at 17:30
Hi Nina, Not it wasn't a question really, I was sort of asking whether I answered your question as I wasn't sure that I did.. Thanks for your help. — Yos
– Yos, Commented Nov 5, 2018 at 17:51

Nina Scholz · Accepted Answer · 2018-11-05 17:38:10Z

2

You could reduce the array by using an object and take a default object if the property is not set. Then push the price.

var data = [{ name: "name1", price: "209.67" }, { name: "name1", price: "350" }, { name: "name2", price: "195.97" }],
    result = data.reduce((r, { name, price }) => {
        r[name] = r[name] || { name, prices: [] };
        r[name].prices.push(+price);
        return r;
    }, Object.create(null));
    
console.log(result);

edited Nov 5, 2018 at 17:38

answered Nov 5, 2018 at 17:25

Nina Scholz

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1 Comment

Yos Over a year ago

Thank you very much. I wasn't aware of the reduce function. It works perfect for my needs.

front_end_dev · Accepted Answer · 2018-11-05 18:06:02Z

1

Try this

function parseData(input){
    return input.reduce(function(o,i){
        o[i.name] = {};
        if(!o[i.name]['prices']){
           o[i.name]['prices'] = [];
        }
        o[i.name]['prices'].push(i.prices);
        return o;
    },{});
}

edited Nov 5, 2018 at 18:06

answered Nov 5, 2018 at 17:28

front_end_dev

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3 Comments

Yos Over a year ago

Thank you very much. I wasn't aware of the reduce function. It works perfect for my needs. I'm sorry but I accepted the first answer but i'm pretty sure that both would work. Joe

Nina Scholz Over a year ago

you overwrite prices for the same name.

front_end_dev Over a year ago

@NinaScholz Thanks for pointing out . I have update the answer.

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