javascript object get array of values from array of keys

Question

I have an array of keys: var keys = ["key1","key2","key3"] and an array of Objects:

var objArr= [
    {"key0":1,"key1":2,"key2":3,"key3":4},
    {"key0":5,"key1":6,"key2":7,"key3":8}
]

I want to be able to get the values from the array of objects based off the array of keys. For example, the output of this would be valueArr = [[2,3,4],[6,7,8]]

I've tried the following:

var result = objArr.map(function(a) {
    for (var i=0;i<keys.length;i++){
        return a[keys[i]];
    };
})

but this returns [2,6] because its just returning the first value it gets to. I'm not sure how to fix it so any help is appreciated, thanks!

Answer 1

Push value in array and return array from Array#map

var keys = ["key1", "key2", "key3"];
var objArr = [{
  "key0": 1,
  "key1": 2,
  "key2": 3,
  "key3": 4
}, {
  "key0": 5,
  "key1": 6,
  "key2": 7,
  "key3": 8
}];

var result = objArr.map(function(a) {
  var arr = [];
  for (var i = 0; i < keys.length; i++) {
    arr.push(a[keys[i]]);
  };
  return arr;
});
console.log(result);

Or using Array#map inside Array#map

var keys = ["key1", "key2", "key3"];
var objArr = [{
  "key0": 1,
  "key1": 2,
  "key2": 3,
  "key3": 4
}, {
  "key0": 5,
  "key1": 6,
  "key2": 7,
  "key3": 8
}];

var result = objArr.map(function(a) {
  return keys.map(function(key) {
    return a[key];
  });
});
console.log(result);

Answer 2

don't return too early , the loop only went through the first item :

var result = objArr.map(function(a) {
    var resp = [];
    for (var i=0;i<keys.length;i++){
        resp.push(a[keys[i]]);            
    };
    return resp;
})

Answer 3

As an alternative, you can use Object.values() function, as suggested here. Example:

var objArr= [
    {"key0":1,"key1":2,"key2":3,"key3":4},
    {"key0":5,"key1":6,"key2":7,"key3":8}
];

for(var i in objArr){
    objArr[i] = Object.values(objArr[i]);
}

This is not supported by Internet Explorer, Opera or Safari at the moment though

Answer 4

You coud use nested Array#map.

var keys = ["key1", "key2", "key3"],
    objArr = [{ "key0": 1, "key1": 2, "key2": 3, "key3": 4 }, { "key0": 5, "key1": 6, "key2": 7, "key3": 8 }],
    result = objArr.map(function (a) {
        return keys.map(function (k) {
            return a[k];
        });
    });

console.log(result);

ES6

var keys = ["key1", "key2", "key3"],
    objArr = [{ "key0": 1, "key1": 2, "key2": 3, "key3": 4 }, { "key0": 5, "key1": 6, "key2": 7, "key3": 8 }],
    result = objArr.map(a => keys.map(k => a[k]));

console.log(result);

Answer 5

You need to push the values onto an array, return will immediately break out of execution and return the value.

Try this:

var result = objArr.map(function(a) {
    var res = [];
    for (var i=0;i<keys.length;i++){
        res.push(a[keys[i]]);
    };
    return res;
})