Extracting an object from an array in Javascript

Question

I am working on a D3.JS chart using an array named "dataset" where each entry is an object with a key and value attributes, such as the following:

dataset= 
 [
 {"key":"alpha", "value": [ {}, { } ...]},
 {"key":"beta", "value": [ { }, { } ...]},
 {"key":"gamma", "value": [ {}, { } ...]},
 {"key":"delta", "value": [ { }, { } ...]}
 ];

I need to extract one of those objects to create a new array. I have tried the following:

filteredDataset = dataset.filter(function(d){ console.log("d",d); if(d.key === "gamma") return d});

I can see in the console that I am accessing each object in the dataset, but the resulting filteredDataset comes out empty. What am I doing wrong?

Your code is correct. I tested it and there isn't any issues. — vivek_nk
– vivek_nk, Commented Apr 10, 2014 at 5:15

Matyas · Accepted Answer · 2014-04-10 05:18:54Z

1

For clarity filter should be used by returning a boolean:

Like:

filteredDataset = dataset.filter(function(d){ return d.key === "gamma"})

And on my end the code

var dataset = [
     {"key":"alpha", "value": [ {}, { }]},
     {"key":"beta", "value": [ { }, { }]},
     {"key":"gamma", "value": [ {}, { }]},
     {"key":"delta", "value": [ { }, { }]}
]; 
filteredDataset = dataset.filter(function(d){ return d.key === "gamma"})

Outputs:

[ { key: 'gamma', value: [ {}, {} ] } ]

So please double check your code

answered Apr 10, 2014 at 5:18

Matyas

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2 Comments

mfroese Over a year ago

Matyas and @thefoureye: For some reason, my code was giving me a null array as result of the filtered dataset. I did the changes that Matyas suggested and it works!!! Thanks, do you have any ideas why the code was not working for me in the first place?

Matyas Over a year ago

Sorry but I don't have any ideas why the other way did not work. Because essentially you may return any object that evaluates to true, so your code should've been valid as well

Rick Lancee · Accepted Answer · 2014-04-10 05:27:06Z

0

dataset.filter(function(d){return d.key === 'gamma';});
This returns the data where key === gamma.

https://github.com/mbostock/d3/wiki/Selections#filter

answered Apr 10, 2014 at 5:27

Rick Lancee

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