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javascriptarraysjsonperformancealgorithm
john Smith
john Smith

Reputation: 1605

javascript - extract array from json object

Let say We have the following json object:

[{"a1" : "a1Val", "a2" : "a2Val", "a3" : "a3Val"}, 
 {"b1" : "b1Val", "b2" : "b2Val", "b3" : "b3Val"},

 ....

 {"z1" : "z1Val", "z2" : "z2Val", "z3" : "z3Val"}]

How can we retrieve from this object array of only X2 key value pairs.

meaning, the following result:

 [ {"a2" : "a2Val"}, {"b2" : "b2Val"}, ... ,{ "z2" : "z2Val"}]

within the best performance.

The key does not have to contains number.

What I need here is a function that will recieve parameter - i and return an array of all the i-th objects in the original json object

So for example if we look at the above json object and we invoke the method we 2 the method will return

 [ {"a2" : "a2Val"}, {"b2" : "b2Val"}, ... ,{ "z2" : "z2Val"}]

Hope it's clear enough.

Upvotes: 0

Views: 26979

Answers (7)

Vasanth
Vasanth

Reputation: 210

var initialArr = [
                  {"a1" : "a1Val", "a2" : "a2Val", "a3" : "a3Val"}, 
                  {"b1" : "b1Val", "b2" : "b2Val", "b3" : "b3Val"},
                  {"z1" : "z1Val", "z2" : "z2Val", "z3" : "z3Val"}
                 ];

var resArr = initialArr.map(function(x){
    return x[Object.keys(x)[1]];
});

jsFiddle Demo

Here in this resArr, I am mapping it to initialArr[ ], to generate an array out of it called resArr and the each element initialArr is represented as 'x' in this x is an object now inorde to get the 2nd element of the object x[1] so here, 1 represents the second element as index starts from 0,1 ,,,so we need to get the keys of that object by Object.keys(x)[1]...hence value would be x[Object.keys(x)[1]].

Upvotes: 3

Xotic750
Xotic750

Reputation: 23482

You will probably find that it is more efficient to do this when parsing your JSON string by using a reviver function. Something like this.

var json = '[{"a1" : "a1Val", "a2" : "a2Val", "a3" : "a3Val"},{"b1" : "b1Val", "b2" : "b2Val", "b3" : "b3Val"},{"z1" : "z1Val", "z2" : "z2Val", "z3" : "z3Val"}]',
    data = JSON.parse(json, function (key, value) {
        if (key !== "" && typeof value === 'object') {
            Object.keys(value).forEach(function (name) {
                if (name.slice(-1) !== '2') {
                    delete value[name];
                }
            });
        }

        return value;
    });

document.body.appendChild(document.createTextNode(JSON.stringify(data)));

Upvotes: 1

Qwerty
Qwerty

Reputation: 31949

Just a really fancy way to do exactly what you asked. Applicable to anything after little tweaking

var json   = '[{"a1" : "a1Val", "a2" : "a2Val", "a3" : "a3Val"},{"b1" : "b1Val", "b2" : "b2Val", "b3" : "b3Val"},{"z1" : "z1Val", "z2" : "z2Val", "z3" : "z3Val"}]',
    parsed = JSON.parse(json),
    index  = 2, // here goes your value

    result = parsed.map(function(obj){
               var key = Object.keys(obj)[0][0]+index,
                   retDict = {};
               return retDict[key] = obj[key], retDict;
             });

Run this in a console and see.

Upvotes: 1

Exinferis
Exinferis

Reputation: 687

What about this:

var collection, key, obj, objArr, _i, _len, _tmp;

collection = [
  {
    "a1": "a1Val",
    "a2": "a2Val",
    "a3": "a3Val"
  }, {
    "b1": "b1Val",
    "b2": "b2Val",
    "b3": "b3Val"
  }
];

objArr = [];

for (_i = 0, _len = collection.length; _i < _len; _i++) {
  obj = collection[_i];
  for (key in obj) {
    _tmp = {};
    _tmp[key] = obj[key];
    objArr.push(_tmp);
  }
}

Upvotes: 0

Amit Joki
Amit Joki

Reputation: 59232

You could use Array.map here

var arr = oldArr.map(function(obj){
    var key = Object.keys(obj).sort()[1], rtn = {};    
    return rtn[key] = obj[key], rtn;
});

What you're doing is taking the second key and then returning a new Object with that key and value.

Upvotes: 9

lante
lante

Reputation: 7336

Convert to array, map the keys, filter results, concat it all, etc. This should work for you:

var result = arr
    .map(function (obj) { 
        return Object.keys(obj).map(function (key) {
            var result = {};
            result[key] = obj[key];

            if (key.substring(1) === "2") {
                return result;
            }
        });
    })
    .reduce(function (x, y) { return x.concat(y); }, [])
    .filter(function (obj) { return obj });

See working fiddle.

Upvotes: 0

Dante
Dante

Reputation: 63

Do a forEach loop on the array. Then for each value get the key with a regular expression. (Loop through object get value using regex key matches Javascript). I won't give you the full code because it is easy to implement and it is a good learning experience.

Upvotes: 0

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