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.

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.

• javascript
• arrays

• 1 See here: stackoverflow./questions/18912/how-to-find-keys-of-a-hash – 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 -- Commented Sep 3, 2013 at 17:09
• 1 Object.keys(groupedDataSet1[i]).length should do the trick. – raina77ow Commented Sep 3, 2013 at 17:09

2 Answers 2

Object.keys(groupedDataSet[0]).length

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

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"]