How to randomly select numbers within an arbitrary range and add together using JavaScript arrays

Question

I am trying to write some JavaScript that will select some random numbers from an array and then add those selected numbers to make a single total value.

For example if i had var array = [1, 22, 5, 88, 3, 105, 7, 88, 987] i would then like the code to select however many numbers it wants at random(amount selected changes every time it runs) and then add them together but i am not sure if this is even possible.

I am new to JavaScript so i have only managed to write code that adds all the array elements together instead of selecting at random.

var arr = [1,2,3,4,5,6];
var total=0;
    for(var i in arr) { total += arr[i]; }

My code is very basic so please excuse me for this i'm still learning. Thank You

Here is how to grab a random one, just need to do it every time you need and add the result each time. http://stackoverflow.com/questions/4550505/getting-random-value-from-an-array — GillesC, Nov 26 '14 at 11:56

score 1 · Accepted Answer · edited May 23 '17 at 12:21

1

You could use the Math.rand() function in order to create a random index. In terms of code:

// The array with your elements
var arr = [1,2,3,4,5,6];

// An array that will keep track of the elements we have selected.
var selectedIndex = [];

// The sum.
var sum=0;

// times is the number of elements we want to select from arr and sum them.
for(var i=0; i<times; i++)
{
    // Get a random integer number in the range [0, arr.length]
    var index = Math.floor(Math.rand()*arr.length);

    // check if the index we created has been selected again.
    if(selectedIndex.indexOf(index)>-1)
    {
        // The created index has been selected again. So we must select another one,
        // in order we get an item from the array only once.        
        while(selectedIndex.indexOf(index)>-1)
            index = Math.floor(Math.rand()*arr.length);    
    }

    // We push the created index in the selected index array.
    selectedIndex.push(index);

    // We increase the sum.
    sum+=arr[index];
}

update

In order the above to be executed the caller should provide a value for the variable called times. This value in order to be valid shouldn't exceed the length of the array called arr.

Another way more elegant, it would be to follow on this part the solution that deitch suggested in his post.

var times = Math.floor((Math.random() * arr.length)+1)

The above should be placed just before the for statement.

edited May 23 '17 at 12:21

Community

1
1

answered Nov 26 '14 at 11:58

Christos

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Yeah, I like this one too. As long as you make sure you don't select the same element twice, you are OK. I will upvote this. – deitch Nov 26 '14 at 12:07
Thank you for this :) when i run the code it keeps telling me that times is not defined any ideas? I am using TextPad(not my choice) – Nov 26 '14 at 12:13
@user2982634 you welcome dude ! You have to provide a value for the `times` variable. – Christos Nov 26 '14 at 12:14
oh so i just enter any number instead of the word times? – Nov 26 '14 at 12:15
@user2982634 yup. Provided that this number is not greater than the length of your array. – Christos Nov 26 '14 at 12:16
That is brilliant thank you. I haven't managed to get the code to work in TextPad as some methods not supported but hopefully i will shortly – Nov 26 '14 at 12:34

score 1 · Answer 2 · answered Nov 26 '14 at 12:07

I think you are looking something like:

<code>
function randormTotal() {
             var arr = [1,2,3,4,5,6];
             var total=0;
             var noOfData = 3;
             for(var i =0; i<noOfData; i++) { 
               var pos = Math.floor(Math.random()*(arr.length-1)) + 1;             
               total += arr[pos];
             }
             alert(total);
         }
</code>

score 0 · Answer 3 · answered Nov 26 '14 at 12:07

FYI, this method actually modifies the array, so you might want to copy it.

// randomly select how many elements you will pick
var i, total = 0, elmsCount = Math.floor((Math.random() * arr.length)+1), current;
// select that many elements
for (i=0; i<elmsCount; i++) {
  current = Math.floor(Math.random()*arr.length);
  total += arr.splice(current,1)[0];
}
// total is now the sum

How to randomly select numbers within an arbitrary range and add together using JavaScript arrays

3 Answers3