从JavaScript数组中获取随机X项

Question

I have the following fiddle using test data, and I am looking through data using $.each

I can loop through no problem, but I want to loop through the data, and then get 3 objects from it at random.

Any tips or tricks would help:

https://jsfiddle.net/inkedraskal/pah44qv6/

$.each(testData,function(x, blah){
    //console.log(blah._id);

  //this gets each objects id & picture, but I want to get 3 random objects, and their corresponding data
  var activeValue = blah._id,
        pictureValue = blah.picture;


  var markUp = '';

  markUp += activeValue + pictureValue;

  console.log(markUp);
});

with the question below, they need to be unique**

Answer 1

We can create getRandomEntry() function which will return one of the array's elements by using Math.random() function. We'll create a loop which will take random entry every time it iterates.

function getRandomEntry() {
  return testData[Math.round(Math.random() * (testData.length - 1))];
}

for (var i=0; i<3; i++) {
  var entry = getRandomEntry();
  console.log(entry._id, entry.picture);
}

If you need an unique entry every time. You can keep random entries in separate array and check if new one is unqiue.

var randomEntries = [];

function getRandomEntry() {
  return testData[Math.round(Math.random() * (testData.length - 1))];
}

function entryExists(entry) {
  return randomEntries.indexOf(entry) > -1;
}

for (var i=0; i<3; i++) {
  var entry;

  do {

    entry = getRandomEntry();

  } while(entryExists(entry))

  randomEntries.push(entry);
  console.log(entry._id, entry.picture);
}

Answer 2

The function in the snippet below gets an array and a number (X) of items and returns a new array with X unique random items from the original array:

 function getRandomItems(arr, items) { var ret = []; var indexes = []; var arr_length = arr.length; // If we don't have enough items to return - return the original array if (arr_length < items) { return arr; } while (ret.length < items) { i = Math.floor(Math.random() * arr_length); if (indexes.indexOf(i) == -1) { indexes[indexes.length] = i; ret[ret.length] = arr[i]; } } return ret; } arr = ['a', 'b', 'c', 'd', 'e'] console.log(getRandomItems(arr, 2)) 

You can also add the function to the Array.prototype if you want to use it on every Array in your code as a "native" function:

 Array.prototype.getRandomItems = function(items) { var ret = []; var indexes = []; var arr_length = this.length; // If we don't have enough items to return - return the original array if (arr_length < items) { return this; } while (ret.length < items) { i = Math.floor(Math.random() * arr_length); if (indexes.indexOf(i) == -1) { indexes[indexes.length] = i; ret[ret.length] = this[i]; } } return ret; } arr1 = ['a', 'b', 'c', 'd', 'e'] arr2 = ['aaa', 'bbb', 'ccc', 'ddd', 'eee'] console.log(arr1.getRandomItems(1)) console.log(arr1.getRandomItems(2)) console.log(arr2.getRandomItems(3)) console.log(arr2.getRandomItems(4)) 

Answer 3

You could use a recursive function like the below.

Note that this implementation prevents duplicates in the results

 function getRandomObjects(array,selected,needed){ /* *@param array array The array to pull from *@param selected array The array of results pulled so far *@param needed int The number of results we want */ var length = array.length; var num = Math.floor(Math.random() * length) + 1; // get random number in bounds of array var exists=false; // make sure we didnt already pick this object $.each(selected,function(i,obj){ if(obj.index==num)exists=true; }) if(exists) getRandomObjects(array,selected,needed); // get a new one if this was a duplicate else selected.push(array[num]); if(selected.length!=needed) return getRandomObjects(array,selected,needed); // get another object if we need more else return selected; // return the final result set } var testData = [ { "_id": "57e5d1a90c4206b128cd8654", "index": 0, "guid": "1f3269fc-0822-4c5a-9c52-8055155b407e", "isActive": true, "balance": "$3,026.95", "picture": "http://placehold.it/32x32" }, { "_id": "57e5d1a9a986ccb2f41cf7b9", "index": 1, "guid": "a6b726b6-6466-4e48-8697-1c6bd7b1c79e", "isActive": true, "balance": "$2,642.74", "picture": "http://placehold.it/32x32" }, { "_id": "57e5d1a9f98f8b2f6880de32", "index": 2, "guid": "e7d736cc-19e0-4bcb-8d0a-4d17442d8cee", "isActive": true, "balance": "$3,341.64", "picture": "http://placehold.it/32x32" }, { "_id": "57e5d1a9e40ded5b017e45cd", "index": 3, "guid": "64230ca8-05c0-4c39-a931-794172475a32", "isActive": true, "balance": "$2,196.13", "picture": "http://placehold.it/32x32" }, { "_id": "57e5d1a90cc30be769a06d7c", "index": 4, "guid": "d6618b78-753a-4ad0-bc14-3687d0b99196", "isActive": true, "balance": "$1,611.62", "picture": "http://placehold.it/32x32" }, { "_id": "57e5d1a92481a43f50607415", "index": 5, "guid": "35ec8186-9494-4f89-ab89-bed7f39872c3", "isActive": true, "balance": "$3,148.87", "picture": "http://placehold.it/32x32" }, { "_id": "57e5d1a9164f17c558ba7ce1", "index": 6, "guid": "244970a0-1ce2-405a-8d69-c7903f9bf5eb", "isActive": false, "balance": "$3,758.13", "picture": "http://placehold.it/32x32" }, { "_id": "57e5d1a95afde31c5cf592a8", "index": 7, "guid": "aa30c82d-dd2b-420c-8b30-7d66cec8d10b", "isActive": true, "balance": "$1,311.40", "picture": "http://placehold.it/32x32" } ] var randomObjects=getRandomObjects(testData,[],3); console.log(randomObjects); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 

Answer 4

You can do this

var items = [1, 2, 3, 4, 5];
var newItems = [];

for(var i = 0; i < 3; i++) {
    var idx = Math.floor(Math.random() * items.length);
    newItems.push(items[idx]);
    items.splice(idx, 1);
}

console.log(newItems);