Transform a key, value object to values only array

Question

What is the best way to transform a key : value object to values only array in Javascript? I'm trying to perform a mongoose query using $in. As far as I know, I need to transform this:

[ { "key": "54ce3bef2d1ce6a82c90ccc3" }, { "key": "54d290a23eff5da01d05fe53" } ]

to this:

[ "54ce3bef2d1ce6a82c90ccc3", "54d290a23eff5da01d05fe53" ]

Should I loop through the first one and then create the second one in the loop? Or should I use some map function (eg. $.map())? Is it wise to perform this operation client side or should I do all the work server side? Source object can grow as much as a few thousand pairs.

Paul S. · Accepted Answer · 2015-02-26 14:28:29Z

1

You can do this quickly for known keys with Array.prototype.map

var arr = [{"key": "54ce3bef2d1ce6a82c90ccc3"}, {"key": "54d290a23eff5da01d05fe53"}];

arr = arr.map(function (e) {return e.key;});
// ["54ce3bef2d1ce6a82c90ccc3", "54d290a23eff5da01d05fe53"]

If the key is unknown but you know there is only one per item, combine with a for..in

arr = arr.map(function (e) {
    var key;
    for (key in e) // may also want to Object.prototype.hasOwnProperty here
        return e[key];
});
// ["54ce3bef2d1ce6a82c90ccc3", "54d290a23eff5da01d05fe53"]

answered Feb 26, 2015 at 14:28

Paul S.

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Ryan · Accepted Answer · 2015-02-26 14:29:53Z

1

Tough call, but my first inclination would be to do a loop, but do you have to worry about duplicates? Below does not account for that...

var arrayToStoreValues = [];
$.each(queryReturnSet,function(i,e){
     arrayToStoreValues[i] = e.key;
});

answered Feb 26, 2015 at 14:29

Ryan

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1 Comment

marcieng Over a year ago

No duplicates. I decided to use arr.map approach. But still not sure which is better from performance perspective. Also not sure about doing this in an angular controller or in the node side is better.

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