Extract array from one json variable

Question

My question seems so simple to me that I cannot figure why I could not find an answer on the web. Really sorry in advance if this has been answered a thousand times, maybe I just don't have the wording right.

I am working with json formatted data in d3.js.

dataset = [
    {"category":"Fiction", "popularity":20},
    {"category":"Thriller", "popularity":45},
    {"category":"Romance", "popularity":12}
];

From all I know, some of the d3.js functions require a simple array.

Example 1: for a bar chart, my d3.scale.ordinal().domain(data) needs an array with ["Fiction", "Thriller", "Romance"]

Example 2: for a pie chart, the d3.layout.pie(data) function needs an array with [20,45,12]

These functions force me to extract all the values from "category" or "popularity" into one-dimensional array via simple for loop, which seems quite dumb.

Is there a more elegant and quick solution to extract an array with the values of one variable from a json?

Thanks a lot for your help! Xavier

That's not JSON, it's an object. You can use .map() to extract the values, but you'd need two .map() statements in a row to create both the ["Fiction","Thriller","Romance"] and [20,45,12] arrays, so I would guess a simple for loop would be more efficient. — nnnnnn
– nnnnnn, Commented Jun 10, 2013 at 12:10

Bruno · Accepted Answer · 2013-06-10 12:31:17Z

3

Use

var category = dataset.map( function( obj ) { return obj.category; } );
var popularity = dataset.map( function( obj ) { return obj.popularity; } );

The category and popularity arrays will contain the values you need.

However, a for loop is likely to be a faster implementation.

edited Jun 10, 2013 at 12:31

answered Jun 10, 2013 at 12:09

Bruno

5,8222 gold badges29 silver badges44 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

xav Over a year ago

Thanks a lot Bruno, I found the answer here (stackoverflow.com/questions/15783475/…) as well as soon as I was done posting :)

nnnnnn Over a year ago

Surely a simple for loop would be more efficient than two .map() statements in a row? And it would end up with about the same amount of code to be typed... Using .map() is (arguably) "more elegant", but it doesn't win on "quick".

Bruno Over a year ago

@nnnnnn You are correct a for loop is likely to be more efficient. However as xav was looking for an alternative to a for loop hence my suggestion. Nonetheless I think the idea to mention the performance implications is important. Thanks.

nnnnnn Over a year ago

Well I gave you an upvote anyway, because like you said the OP was looking for a non-loop (or at least a non-explicit loop) solution. Just wanted to make sure performance got a mention too.

Collectives™ on Stack Overflow

Extract array from one json variable

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related