How to access javascript key/value pairs in an array

Question

I have the following javascript array:

var groupedDataSet1 = [{year: "0-1k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())},
            {year: "1-2k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())},
            {year: "2-3k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())},
            {year: "3-4k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())},
            {year: "4-5k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())}];

I'd like to programatically know how many key/value pairs I have in each entry.

Is there a way to know that groupedDataSet contains the keys year, value1, value2, and value3 while another javascript array might only contain year, value1 and value2?

Doing groupedDataSet[0].length doesn't work.

Thanks.

See here: stackoverflow.com/questions/18912/how-to-find-keys-of-a-hash — just_dont
– just_dont, Commented Sep 3, 2013 at 17:08
A object hash does not have the length property.. you will have to explicitly iterate over the keys to get the length — Sushanth --
– Sushanth --, Commented Sep 3, 2013 at 17:09
Object.keys(groupedDataSet1[i]).length should do the trick. — raina77ow
– raina77ow, Commented Sep 3, 2013 at 17:09

Chris Tavares · Accepted Answer · 2013-09-03 17:10:23Z

3

Object.keys(groupedDataSet[0]).length

should get you what you're looking for. It returns an array containing the instance keys in the object.

answered Sep 3, 2013 at 17:10

Chris Tavares

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2 Comments

Nitzan Wilnai Over a year ago

Once I have the key saved in a variable, how do I access the value? For example key = Object.keys(groupedDataSet[0]). How do I use key to get the actual value stored in groupedDataSet[0].<whatever key is> ?

Nitzan Wilnai Over a year ago

Figured it out. Object.keys(groupedDataSet[0])[key] will return me the value. Thanks!

zs2020 · Accepted Answer · 2013-09-03 17:29:29Z

1

If the objects in the list may have different key set, then you have to check each object to collect all keys. You can do

var keys_memo = {};
groupedDataSet1.forEach(function (item) {
    for (var i in item) {
        keys_memo[i] = 1;
    }
});
var keys = Object.keys(keys_memo);

console.log(keys)
>>>["year", "value1", "value2", "value3"]

edited Sep 3, 2013 at 17:29

answered Sep 3, 2013 at 17:16

zs2020

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