I have an object in JavaScript:
{
abc: '...',
bca: '...',
zzz: '...',
xxx: '...',
ccc: '...',
// ...
}
I want to use a for loop to get its properties. And I want to iterate it in parts (not all object properties at once).
With a simple array I can do it with a standard for loop:
for (i = 0; i < 100; i++) { ... } // first part
for (i = 100; i < 300; i++) { ... } // second
for (i = 300; i < arr.length; i++) { ... } // last
But how to do it with objects?
For iterating on keys of Arrays, Strings, or Objects, use for .. in :
for (let key in yourobject) {
console.log(key, yourobject[key]);
}
With ES6, if you need both keys and values simultaneously, do
for (let [key, value] of Object.entries(yourobject)) {
console.log(key, value);
}
To avoid logging inherited properties, check with hasOwnProperty :
for (let key in yourobject) {
if (yourobject.hasOwnProperty(key)) {
console.log(key, yourobject[key]);
}
}
You don't need to check hasOwnProperty when iterating on keys if you're using a simple object (for example one you made yourself with {}).
This MDN documentation explains more generally how to deal with objects and their properties.
If you want to do it "in chunks", the best is to extract the keys in an array. As the order isn't guaranteed, this is the proper way. In modern browsers, you can use
let keys = Object.keys(yourobject);
To be more compatible, you'd better do this :
let keys = [];
for (let key in yourobject) {
if (yourobject.hasOwnProperty(key)) keys.push(key);
}
Then you can iterate on your properties by index: yourobject[keys[i]] :
for (let i=300; i < keys.length && i < 600; i++) {
console.log(keys[i], yourobject[keys[i]]);
}
Here is another iteration solution for modern browsers:
Object.keys(obj)
.filter((k, i) => i >= 100 && i < 300)
.forEach(k => console.log(obj[k]));
Or without the filter function:
Object.keys(obj).forEach((k, i) => {
if (i >= 100 && i < 300) {
console.log(obj[k]);
}
});
However you must consider that properties in JavaScript object are not sorted, i.e. have no order.
Using Object.entries you do something like this.
// array like object with random key ordering
const anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.entries(anObj)); // [ ['2', 'b'],['7', 'c'],['100', 'a'] ]
The Object.entries() method returns an array of a given object's own enumerable property [key, value]
So you can iterate over the Object and have key and value for each of the object and get something like this.
const anObj = { 100: 'a', 2: 'b', 7: 'c' };
Object.entries(anObj).map(obj => {
const key = obj[0];
const value = obj[1];
// do whatever you want with those values.
});
or like this
// Or, using array extras
Object.entries(obj).forEach(([key, value]) => {
console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
});
For a reference have a look at the MDN docs for Object Entries
With the new ES6/ES2015 features, you don't have to use an object anymore to iterate over a hash. You can use a Map. Javascript Maps keep keys in insertion order, meaning you can iterate over them without having to check the hasOwnProperty, which was always really a hack.
Iterate over a map:
var myMap = new Map();
myMap.set(0, "zero");
myMap.set(1, "one");
for (var [key, value] of myMap) {
console.log(key + " = " + value);
}
// Will show 2 logs; first with "0 = zero" and second with "1 = one"
for (var key of myMap.keys()) {
console.log(key);
}
// Will show 2 logs; first with "0" and second with "1"
for (var value of myMap.values()) {
console.log(value);
}
// Will show 2 logs; first with "zero" and second with "one"
for (var [key, value] of myMap.entries()) {
console.log(key + " = " + value);
}
// Will show 2 logs; first with "0 = zero" and second with "1 = one"
or use forEach:
myMap.forEach(function(value, key) {
console.log(key + " = " + value);
}, myMap)
// Will show 2 logs; first with "0 = zero" and second with "1 = one"
If you want the key and value when iterating, you can use a for...of loop with Object.entries.
const myObj = {a: 1, b: 2}
for (let [key, value] of Object.entries(myObj)) {
console.log(`key=${key} value=${value}`)
}
// output:
// key=a value=1
// key=b value=2
The only reliable way to do this would be to save your object data to 2 arrays, one of keys, and one for the data:
var keys = [];
var data = [];
for (var key in obj) {
if (obj.hasOwnProperty(key)) {
keys.push(key);
data.push(obj[key]); // Not necessary, but cleaner, in my opinion. See the example below.
}
}
You can then iterate over the arrays like you normally would:
for(var i = 0; i < 100; i++){
console.log(keys[i], data[i]);
//or
console.log(keys[i], obj[keys[i]]); // harder to read, I think.
}
for(var i = 100; i < 300; i++){
console.log(keys[i], data[i]);
}
I am not using Object.keys(obj), because that's IE 9+.
->if we iterate over a JavaScript object using and find key of array of
objects
Object.keys(Array).forEach(key => {
console.log('key',key)
})
If you have a simple object you can iterate through it using the following code:
let myObj = {
abc: '...',
bca: '...',
zzz: '...',
xxx: '...',
ccc: '...',
// ...
};
let objKeys = Object.keys(myObj);
//Now we can use objKeys to iterate over myObj
for (item of objKeys) {
//this will print out the keys
console.log('key:', item);
//this will print out the values
console.log('value:', myObj[item]);
}
If you have a nested object you can iterate through it using the following code:
let b = {
one: {
a: 1,
b: 2,
c: 3
},
two: {
a: 4,
b: 5,
c: 6
},
three: {
a: 7,
b: 8,
c: 9
}
};
let myKeys = Object.keys(b);
for (item of myKeys) {
//print the key
console.log('Key', item)
//print the value (which will be another object)
console.log('Value', b[item])
//print the nested value
console.log('Nested value', b[item]['a'])
}
If you have array of objects you can iterate through it using the following code:
let c = [
{
a: 1,
b: 2
},
{
a: 3,
b: 4
}
];
for(item of c){
//print the whole object individually
console.log('object', item);
//print the value inside the object
console.log('value', item['a']);
}
const o = {
name: "Max",
location: "London"
};
for (const [key, value] of Object.entries(o)) {
console.log(`${key}: ${value}`);
}
Try online
Define object in arguments and avoid selectors & subscripts
There are a number of syntax choices but this one defines the object upfront in the closure's arguments which eliminates the need for selectors or subscripts in the iterator. k is key, v is value, i is index.
const obj = {
kiwi: true,
mango: false,
pineapple: 500
};
Object.entries(obj).forEach(([k, v], i) => {
console.log(k, v, i);
});
// kiwi true 0
// mango false 1
// pineapple 500 2
If you wanted to iterate the whole object at once you could use for in loop:
for (var i in obj) {
...
}
But if you want to divide the object into parts in fact you cannot. There's no guarantee that properties in the object are in any specified order. Therefore, I can think of two solutions.
First of them is to "remove" already read properties:
var i = 0;
for (var key in obj) {
console.log(obj[key]);
delete obj[key];
if ( ++i > 300) break;
}
Another solution I can think of is to use Array of Arrays instead of the object:
var obj = [['key1', 'value1'], ['key2', 'value2']];
Then, standard for loop will work.
I finally came up with a handy utility function with a unified interface to iterate Objects, Strings, Arrays, TypedArrays, Maps, Sets, (any Iterables).
const iterate = require('#a-z/iterate-it');
const obj = { a: 1, b: 2, c: 3 };
iterate(obj, (value, key) => console.log(key, value));
// a 1
// b 2
// c 3
https://github.com/alrik/iterate-javascript
Really a PITA this is not part of standard Javascript.
/**
* Iterates the keys and values of an object. Object.keys is used to extract the keys.
* #param object The object to iterate
* #param fn (value,key)=>{}
*/
function objectForEach(object, fn) {
Object.keys(object).forEach(key => {
fn(object[key],key, object)
})
}
Note: I switched the callback parameters to (value,key) and added a third object to make the API consistent other APIs.
Use it like this
const o = {a:1, b:true};
objectForEach(o, (value, key, obj)=>{
// do something
});
For object iteration we usually use a for..in loop. This structure will loop through all enumerable properties, including ones who are inherited via prototypal inheritance. For example:
let obj = {
prop1: '1',
prop2: '2'
}
for(let el in obj) {
console.log(el);
console.log(obj[el]);
}
However, for..in will loop over all enumerable elements and this will not able us to split the iteration in chunks. To achieve this we can use the built in Object.keys() function to retrieve all the keys of an object in an array. We then can split up the iteration into multiple for loops and access the properties using the keys array. For example:
let obj = {
prop1: '1',
prop2: '2',
prop3: '3',
prop4: '4',
};
const keys = Object.keys(obj);
console.log(keys);
for (let i = 0; i < 2; i++) {
console.log(obj[keys[i]]);
}
for (let i = 2; i < 4; i++) {
console.log(obj[keys[i]]);
}
Yes. You can loop through an object using for loop. Here is an example
var myObj = {
abc: 'ABC',
bca: 'BCA',
zzz: 'ZZZ',
xxx: 'XXX',
ccc: 'CCC',
}
var k = Object.keys (myObj);
for (var i = 0; i < k.length; i++) {
console.log (k[i] + ": " + myObj[k[i]]);
}
NOTE: the example mentioned above will only work in IE9+. See Objec.keys browser support here.
Here is a Hand Made Solution:
function iterationForObject() {
let base = 0,
Keys= Object.keys(this);
return {
next: () => {
return {
value: {
"key": Keys[base],
"value": this[Keys[base]]
},
done: !(base++ < Keys.length)
};
}
};
}
Object.prototype[Symbol.iterator] = iterationForObject;
And Then You Can Loop Any Object:
for ( let keyAndValuePair of (Object Here) ) {
console.log(`${keyAndValuePair.key} => ${keyAndValuePair.value}`);
}
<script type="text/javascript">
// method 1
var images = {};
images['name'] = {};
images['family'] = {};
images[1] = {};
images['name'][5] = "Mehdi";
images['family'][8] = "Mohammadpour";
images['family']['ok'] = 123456;
images[1][22] = 2602;
images[1][22] = 2602;
images[1][22] = 2602;
images[1][22] = 2602;
images[1][23] = 2602;
for (const [key1, value1] of Object.entries(images)){
for (const [key2, value2] of Object.entries(value1)){
console.log(`${key1} => ${key2}: ${value2}`);
}
}
console.log("=============================");
// method 2
var arr = [];
for(var x = 0; x < 5; x++){
arr[x] = [];
for(var y = 0; y < 5; y++){
arr[x][y] = x*y;
}
}
for(var i = 0; i < arr.length; i++) {
var cube = arr[i];
for(var j = 0; j < cube.length; j++) {
console.log("cube[" + i + "][" + j + "] = " + cube[j]);
}
}
</script>
var Dictionary = {
If: {
you: {
can: '',
make: ''
},
sense: ''
},
of: {
the: {
sentence: {
it: '',
worked: ''
}
}
}
};
function Iterate(obj) {
for (prop in obj) {
if (obj.hasOwnProperty(prop) && isNaN(prop)) {
console.log(prop + ': ' + obj[prop]);
Iterate(obj[prop]);
}
}
}
Iterate(Dictionary);
You can try using lodash- A modern JavaScript utility library delivering modularity, performance & extras js to fast object iterate:-
var users = {
'fred': {
'user': 'fred',
'age': 40
},
'pebbles': {
'user': 'pebbles',
'age': 1
}
};
_.mapValues(users, function(o) {
return o.age;
});
// => { 'fred': 40, 'pebbles': 1 } (iteration order is not guaranteed)
// The `_.property` iteratee shorthand.
console.log(_.mapValues(users, 'age')); // returns age property & value
console.log(_.mapValues(users, 'user')); // returns user property & value
console.log(_.mapValues(users)); // returns all objects
// => { 'fred': 40, 'pebbles': 1 } (iteration order is not guaranteed)
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash-compat/3.10.2/lodash.js"></script>
Related
hi all i am using javascript working with array i have a set of data to do add array values object here i attached my code help how to solve this
data
var data=[{one:1,two:2},{one:1,two:2},{one:1,two:2},{one:1,two:2}]
expected output
var sumdata=[{one:4,two:8}]
NOTE:one two column name is not static
var resObj = {};
for (var i = 0; i < data.length; i++) {
for (var item in data[i]) {
if (!resObj.hasOwnProperty(item)) {
resObj[item] = data[i][item];
} else {
resObj[item] += data[i][item];
}
}
}
var sumdata = [resObj];
You could use an object as result and iterate the keys of the object and sum the values.
var data = [{ one: 1, two: 2 }, { one: 1, two: 2 }, { one: 1, two: 2 }, { one: 1, two: 2 }],
result = data.reduce(function (r, o) { // iterate array
Object.keys(o).forEach(function (k) { // iterate the keys of the object
r[k] = (r[k] || 0) + o[k]; // check if a property exists or take zero
}); // and add the actual value
return r; // return the object
}, Object.create(null)); // start with an empty object without
// some prototypes
console.log(result);
I have a JavaScript object array. When write console.log(myarry) it will show in the console in the below form.
Array[2]
0: Object
one: "one"
1: Object
two: "two"
length: 2
In this array my key and value are same and am trying to get the key or value to a variable and print it. When am trying the below code it showing:
object object
for (var key in myarry) {
alert("Key is " + key + ", value is" + myarry[key]);
}
check this snippet
var obj = [{
"1": "one"
}, {
"2": "two"
}]
obj.forEach(function(item) {
Object.keys(item).forEach(function(key) {
console.log("key:" + key + "value:" + item[key]);
});
});
Hope it helps
Use for-loop instead of for-in to iterate array.
Use Object.keys to get keys of object
var arr = [{
one: 'one'
}, {
two: 'two'
}];
for (var i = 0, l = arr.length; i < l; i++) {
var keys = Object.keys(arr[i]);
for (var j = 0, k = keys.length; j < k; j++) {
console.log("Key:" + keys[j] + " Value:" + arr[i][keys[j]]);
}
}
I think you have two main options to get keys of an object using Object.keys these are: forEach; or a simple for.
1. Use forEach
If you're using an environment that supports the Array features of ES5 (directly or using a shim), you can use the new forEach:
var myarray = [{one: 'one'}, {two: 'two'}];
myarray.forEach(function(item) {
var items = Object.keys(item);
items.forEach(function(key) {
console.log('this is a key-> ' + key + ' & this is its value-> ' + item[key]);
});
});
forEach accepts an iterator function and, optionally, a value to use as this when calling that iterator function (not used above). The iterator function is called for each entry in the array, in order, skipping non-existent entries in sparse arrays. Although
forEach has the benefit that you don't have to declare indexing and value variables in the containing scope, as they're supplied as arguments to the iteration function, and so nicely scoped to just that iteration.
If you're worried about the runtime cost of making a function call for each array entry, don't be; technical details.
2. Use a simple for
Sometimes the old ways are the best:
var myarray = [{one: 'one'}, {two: 'two'}];
for (var i = 0, l = myarray.length; i < l; i++) {
var items = myarray[i];
var keys = Object.keys(items);
for (var j = 0, k = keys.length; j < k; j++) {
console.log('this is a key-> ' + keys[j] + ' & this is its value-> ' + items[keys[j]]);
}
}
Depending on your construction, you can do
const arr = [{ key1: 'val1' }, { key2: 'val2' }]
arr.forEach((a, i) =>
console.log(i, [{ key: Object.keys(a) }, { val: Object.values(a) }])
)
and to answer your question
arr.forEach((a, i) =>
alert("Key is "+ Object.keys(a) + ", value is " + Object.values(a))
)
am trying to get the key or value to a variable and print it.
then you could
var myarry = [{ one: 'one' }, { two: 'two' }];
for (var key in myarry) {
var value = myarry[key];
console.log(key, value)
}
you can do it in this way
const a = [{ one: 'one' }, { two: 'two' }];
a.forEach(function(value,key) {
console.log(value,key);
});
You can take key and value in a variable and use them.
Here's an interesting way to do it.
const arr = [{ one: 'one' }, { two: 'two' }];
Object.entries(arr).forEach(([_, obj]) => {
const key = Object.keys(obj)[0];
console.log(`Key is ${key}, value is ${obj[key]}.`);
});
sorry, i m a beginner in javascript.
Can someone explain me how to modify this Object
{toto:[12,13,15],titi:[45,12,34]}
to this Array
newArray = [
{
toto:12,
titi:45
},{
toto:13,
titi:12
},{
toto:15,
titi:34}
]
Also, what the solution if the toto and titi doesn't have the same lenght
Thanks for support!
Here's how I did it. In this way, you don't need to know the names of the keys or the size of the array, but it does require a few loops.
obj = {toto:[12,13,15],titi:[45,12,34]};
newArray = [];
// Find the longest array in your data set
longest = 0;
Object.keys(obj).forEach(function(key) {
if (obj[key].length > longest) {
longest = obj[key].length;
}
});
// Loop through the existing data set to create new objects
for (i = 0; i<longest; i++) {
newObject = {};
Object.keys(obj).forEach(function(key) {
newObject[key] = obj[key][i];
});
newArray.push(newObject);
}
console.log(newArray);
plnkr.co demo in the script.js file.
If you want to ignore keys that would have undefined values for uneven loops, you can add a conditional inside the forEach loop that creates a new object:
Object.keys(obj).forEach(function(key) {
if (obj[key][i] !== undefined) {
newObject[key] = obj[key][i];
}
});
Assuming lengths of toto and titi are the same:
Obj = {toto:[12,13,15],titi:[45,12,34]};
newArray = [];
for (var k in Obj["toto"]) {
newArray.push({ toto:Obj["toto"][k],titi:Obj["titi"][k] });
}
Since the lengths of your inner arrays are equal, you should be able to simply loop through them and add a value from each array (for each iteration) into a new array :
// Your input
var input = {toto:[12,13,15],titi:[45,12,34]};
// An array to store your output
var output = [];
// Since your inner arrays are of equal size, you can loop through them
// as follows
for(var i = 0; i < input.toto.length; i++){
output.push({ toto: input.toto[i], titi: input.titi[i]});
}
You can see a working example of this here and what the output array looks like below :
A more generic approach
var object = { toto: [12, 13, 15], titi: [45, 12, 34] },
newArray = function (o) {
var keys = Object.keys(o),
l = keys.reduce(function (r, a) { return Math.max(r, o[a].length); }, 0),
i = 0,
t,
result = [];
while (i < l) {
t = {};
keys.forEach(function (k) { t[k] = o[k][i]; });
result.push(t);
i++;
}
return result;
}(object);
document.write('<pre>' + JSON.stringify(newArray, 0, 4) + '</pre>');
I have an associative array like:
var arr = {};
arr['alz'] = '15a';
arr['aly'] = '16b';
arr['alx'] = '17a';
arr['alw'] = '09c';
I need to find the previous and next key of any selected element. Say, for key 'aly' it will be 'alz' and 'alx'. If possible, I want to access the array by index rather than the key.
Currently, I am doing this using a separate array containing keys, e.g.
var arrkeys = ['alz','aly','alx','alw'];
Ordering of the object's properties is undefined. You can use this structure...
[{ key: 'alz', value: '15a'},
{ key: 'aly', value: '16b'},
{ key: 'alx', value: '17a'}]
... though searching for the element with the given key (like 'give me the element which key is 'alz') is not as straight-forward as with simple object. That's why using it like you did - providing a separate array for ordering of the indexes - is another common approach. You can attach this array to that object, btw:
var arr={};
arr['alz']='15a';
arr['aly']='16b';
arr['alx']='17a';
arr['alw']='09c';
arr._keysOrder = ['alz', 'aly', 'alx', 'alw'];
This is an object, not an array, and it sounds like you don't really want those strings to be keys.
How about a nice array?
var ar = [
{ key: 'alz', value: '15a' },
{ key: 'aly', value: '16b' },
{ key: 'alx', value: '17a' },
{ key: 'alw', value: '09c' }
];
How about adding some syntactic sugar in the form of an OrderedObject object? Then you could do something like this:
myObj = new OrderedObject();
myObj.add('alz', '15a');
myObj.add('aly', '16b');
myObj.add('alx', '17a');
myObj.add('alw', '09c');
console.log(myObj.keyAt(2)); // 'alx'
console.log(myObj.valueAt(3)); // '09c'
console.log(myObj.indexOf('aly')); // 1
console.log(myObj.length()) // 4
console.log(myObj.nextKey('aly')); // 'alx'
The following code makes this work. See it in action in a jsFiddle.
function OrderedObject() {
var index = [];
this.add = function(key, value) {
if (!this.hasOwnProperty(key)) {
index.push(key);
}
this[key] = value;
};
this.remove = function(key) {
if (!this.hasOwnProperty(key)) { return; }
index.splice(index.indexOf(key), 1);
delete this[key];
}
this.indexOf = function(key) {
return index.indexOf(key);
}
this.keyAt = function(i) {
return index[i];
};
this.length = function() {
return index.length;
}
this.valueAt = function(i) {
return this[this.keyAt(i)];
}
this.previousKey = function(key) {
return this.keyAt(this.indexOf(key) - 1);
}
this.nextKey = function(key) {
return this.keyAt(this.indexOf(key) + 1);
}
}
I made some decisions that may not work for you. For example, I chose to use an Object as the prototype rather than an Array, so that you could preserve enumerating your object with for (key in myObj). But it didn't have to be that way. It could have been an Array, letting you use the property .length instead of the function .length() and then offering an each function that enumerates the keys, or perhaps an .object() function to return the inner object.
This could be a little awkward as you'd have to remember not to add items to the object yourself. That is, if you do myObj[key] = 'value'; then the index will not be updated. I also did not provide any methods for rearranging the order of things or inserting them at a particular position, or deleting by position. If you find my object idea useful, though, I'm sure you can figure out how to add such things.
With the newer versions of EcmaScript you can add true properties and make them non-enumerable. This would allow the new object to more seamlessly and smoothly act like the ideal OrderedObject I am imagining.
If you have to know the order of everything, and still use the keys and values, try this:
var arr = [
{ key: 'alz', value: '15a' },
{ key: 'aly', value: '16b' },
{ key: 'alx', value: '17a' },
{ key: 'alw', value: '09c' }
];
You can then access them sequentially as follows: arr[0].key and arr[0].value. Similarly, you can find siblings inside of the loop with the following:
for(var i = 0; i < arr.length; i++)
{
var previous_key = (i > 0) ? arr[(i - 1)].key : false;
var next_key = (i < (arr.length - 1)) ? arr[(i + 1)].key : false;
}
You may try this
function sortObject(obj, order)
{
var list=[], mapArr = [], sortedObj={};
for(var x in obj) if(obj.hasOwnProperty(x)) list.push(x);
for (var i=0, length = list.length; i < length; i++) {
mapArr.push({ index: i, value: list[i].toLowerCase() });
}
mapArr.sort(function(a, b) {
if(order && order.toLowerCase()==='desc')
return a.value < b.value ? 1 : -1;
else return a.value > b.value ? 1 : -1;
});
for(var i=0; i<mapArr.length;i++)
sortedObj[mapArr[i].value]=obj[mapArr[i].value];
return sortedObj;
}
// Call the function to sort the arr object
var sortedArr = sortObject(arr); // Ascending order A-Z
var sortedArr = sortObject(arr, 'desc'); // Descending order Z-A
DEMO.
Remember, this will return a new object and original object will remain unchanged.
I have a data dictionary like this:
var data = {
'text1': 1,
'text2': 2,
'text3': 3,
...
'text20': 20
];
I need to pick a random selection of those keys and then shuffle it's values. In the example, it should write something like this:
> console.log(choose(data, 5));
[ { key: 'text15', value: 8 },
{ key: 'text6', value: 3 },
{ key: 'text3', value: 15 },
{ key: 'text19', value: 6 },
{ key: 'text8', value: 19 } ]
For now I'm extracting the keys into another array and sorting by Math.random() but I'm stuck at swaping the values because no key should have the same value it initially had.
How would you swap key/values here?
Thanks
I put together a possible solution using underscore.js to simplify traversing the object and arrays in a cross browser manner:
var data = {
text1: 1,
text2: 2,
text3: 3,
text4: 4,
text5: 5,
text6: 6,
text7: 7,
text8: 8,
text9: 9,
text10: 10
};
function choose(data, num)
{
var keys = _.sortBy(
_.keys(data),
function(k)
{
return (Math.random() * 3) - 1;
}
),
results = [],
k1, k2;
if (num > keys.length) {
throw new Error('Impossible to retrieve more values than exist');
}
while (results.length < num) {
k1 = k2 || keys.pop();
k2 = keys.pop();
results.push({key:k1, value: data[k2]});
}
return results;
}
console.log(choose(data, 5));
This isn't necessarily an optimal approach but it seems to meet your requirements. I first grab all of the keys and sort them randomly. I then loop through the random keys creating a new object with one key and the following keys value. That way you'll always end up with a different value associated with each key. If you need it to work when the value of num passed in to the function == the number of keys in the data then you'll have to add a little more code - I'll leave that as an exercise for the reader :)
You can have a play with this code on jsfiddle:
http://jsfiddle.net/zVyQW/1/
You could do this:
collect names and corresponding values in two arrays names and values
shuffle both arrays independently of each other
take the first n items of both arrays and combine them
Here’s an example implementation:
Array.prototype.shuffle = function() {
for (var i=this.length-1, j, tmp; i>0; i--) {
j = Math.round(Math.random()*i);
tmp = this[i], this[i] = this[j], this[j] = tmp;
}
return this;
};
function choose(data, number) {
var names = [], values = [], pick = [];
for (var name in data) {
if (data.hasOwnProperty(name)) {
names.push(name);
values.push(data[name]);
}
}
names = names.shuffle(), values = values.shuffle();
for (var i=Math.min(number >>> 0, names.length-1); i>=0; i--) {
pick.push({key: names[i], value: values[i]});
}
return pick;
}
Been a while since this was answered, but I was working on shuffling and found the following to be by far the fastest implementation with an evenly random distribution.
It's fast because it only makes one call to Math.random on each iteration, all the rest is done by property access. It doesn't modify the array, just reassigns values.
function shuffle(a) {
var t, j, i=a.length, rand=Math.random;
// For each element in the array, swap it with a random
// element (which might be itself)
while (i--) {
k = rand()*(i+1)|0;
t = a[k];
a[k]=a[i];
a[i]=t;
}
return a;
}
It uses a combination of three functions (including the Array shuffle prototype method).
Here is the complete code:
var obj = {
"red":"RED",
"blue":"BLUE",
"green":"GREEN",
"yellow":"YELLOW",
"purple":"PURPLE"
};
Array.prototype.shuffle = function(){
for (var i = 0; i < this.length; i++){
var a = this[i];
var b = Math.floor(Math.random() * this.length);
this[i] = this[b];
this[b] = a;
}
}
obj = shuffleProperties(obj); // run shuffle
function shuffleProperties(obj) {
var new_obj = {};
var keys = getKeys(obj);
keys.shuffle();
for (var key in keys){
if (key == "shuffle") continue; // skip our prototype method
new_obj[keys[key]] = obj[keys[key]];
}
return new_obj;
}
function getKeys(obj){
var arr = new Array();
for (var key in obj)
arr.push(key);
return arr;
}
for(key in obj){
alert(key);
}
Check all post,
Best Regards.
Use an implementation of random that randomizes a discrete set of values, such as Math.rand seen here. For each index, randomize Math.rand(index, length-1) to get a list of random indexes, the location off all indices will change.