JS / ES6: Object to Array conversion

Question

One of my node js libraries is returning some data I need in the wrong format like this:

{"a":["1","2"],"b":["3","4"],"c":["5","6"]}

(note that the values don't matter) but I need to loop this array in a way, that I find my B for my A that has a certain value (in this case e.g. '2', I would need '4') and all other parts of my program are so far using arrays like this:

[{"a":"1", "b":"3", "c":"5"}, {"a":"2", "b":"4", "c":"6"}]

and it would be my preferred approach.

Also note that the amount of data in a is always the same as b and c, but itself is variable.

So what would be the "best" way to accomplish this in ES6/JS (before I start messing with for-loops)?

"would be the "best" way"... if this question is holding you up in your progression, then I would strongly encourage you to read this: joelonsoftware.com/articles/fog0000000018.html — Travis J
– Travis J, Commented Nov 23, 2016 at 0:24
The example of using the array shown here has an error, notably "Uncaught SyntaxError: Unexpected token ,". Did you intend that to be an array? I feel it is a critical piece of your question. — Travis J
– Travis J, Commented Nov 23, 2016 at 0:26
@TravisJ yes, it is intended as array. I was just typing it as an example. Also, I know the talk about why use the "best"? First: this particular code would be called quite often, so optimizing it would be good. Second: if we just thought "oh thats good enough" - we wouldn't be where we are now in terms of tech or anything :) — ThexBasic
– ThexBasic, Commented Nov 23, 2016 at 0:43

Robbie Speed · Accepted Answer · 2016-11-23 00:52:42Z

2

If you are looking to transform an object like

{"a":["1","2"],"b":["3","4"],"c":["5","6"]}

Into a array like

[{"a":"1","b":"3","c":"5"},{"a":"2","b":"4","c":"6"}]

Something like this is the simplest way I can think of

function formatData (data) {
  return Object.keys(data).reduce((arr, key) => {
    data[key].forEach((value, i) => {
     const iObj = arr[i] || (arr[i] = {});
     iObj[key] = value;
    });
    return arr;
  }, []);
}

answered Nov 23, 2016 at 0:52

Robbie Speed

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4 Comments

Robbie Speed Over a year ago

You're question had {["a":"1", "b":"3", "c":"5"], ["a":"2", "b":"4", "c":"6"]} which I'm assuming you meant to be [{"a":"1","b":"3","c":"5"},{"a":"2","b":"4","c":"6"}], since the first isn't valid js.

ThexBasic Over a year ago

yes, you are right. I will update this right now. Also big thanks for the quick response, this works perfectly.

Bergi Over a year ago

Wouldn't for in and for (let i=0; i<data[key].length; i++) loops be even simpler?

Robbie Speed Over a year ago

@Bergi not using for in because it wouldn't provide the index, and basic for would add more boilerplate. However I do agree a reduce could be used instead.

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