Getting a random value from a JavaScript array

2楼-- · 2018-12-31 00:58

This work like a charm for me without any repeat.

   var Random_Value = Pick_Random_Value(Array);

function Pick_Random_Value(IN_Array) 
{
    if(IN_Array != undefined && IN_Array.length > 0)
    {
        var Copy_IN_Array = JSON.parse(JSON.stringify(IN_Array));
        if((typeof window.Last_Pick_Random_Index !== 'undefined') && (window.Last_Pick_Random_Index !== false))
        {
            if(Copy_IN_Array[Last_Pick_Random_Index] != undefined)
            {
                Copy_IN_Array.splice(Last_Pick_Random_Index,1);
            }
        }

        var Return_Value = false;

        if(Copy_IN_Array.length > 0)
        {
            var Random_Key = Math.floor(Math.random() * Copy_IN_Array.length);
            Return_Value = Copy_IN_Array[Random_Key];
        }
        else
        {
            Return_Value = IN_Array[Last_Pick_Random_Index];
        }

        window.Last_Pick_Random_Index = IN_Array.indexOf(Return_Value);
        if(window.Last_Pick_Random_Index === -1)
        {
            for (var i = 0; i < IN_Array.length; i++) 
            {
                if (JSON.stringify(IN_Array[i]) === JSON.stringify(Return_Value)) 
                {
                    window.Last_Pick_Random_Index = i;
                    break;
                }
            }
        }


        return Return_Value;
    }
    else
    {
        return false;
    }
}

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余欢

3楼-- · 2018-12-31 01:00

~~ is much faster than Math.Floor(), so when it comes to performance optimization while producing output using UI elements, ~~ wins the game. MORE INFO

var rand = myArray[~~(Math.random() * myArray.length)];

But if you know that the array is going to have millions of elements than you might want to reconsider between Bitwise Operator and Math.Floor(), as bitwise operator behave weirdly with large numbers. See below example explained with the output. MORE INFO

var number = Math.floor(14444323231.2); // => 14444323231
var number = 14444323231.2 | 0; // => 1559421343

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浮光初槿花落

4楼-- · 2018-12-31 01:00

I've found a way around the top answer's complications, just by concatenating the variable rand to another variable that allows that number to be displayed inside the calling of myArray[];. By deleting the new array created and toying around with it's complications, I've come up with a working solution:

<!DOCTYPE html>
<html>
<body>

<p id="demo"></p>

<script>

var myArray = ['January', 'February', 'March', 'April', 'May'];    

var rand = Math.floor(Math.random() * myArray.length);

var concat = myArray[rand];

function random() {
   document.getElementById("demo").innerHTML = (concat);
}
</script>

<button onClick="random();">
Working Random Array generator
</button>

</body>
</html>

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不流泪的眼

5楼-- · 2018-12-31 01:02

Using Faker.js:

const Faker = require('faker');
Faker.random.arrayElement(['January', 'February', 'March']);

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看淡一切

6楼-- · 2018-12-31 01:05

If you have fixed values (like a month name list) and want a one-line solution

var result = ['January', 'February', 'March'][Math.floor(Math.random() * 3)]

The second part of the array is an access operation as described in Why does [5,6,8,7][1,2] = 8 in JavaScript?

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泪湿衣

7楼-- · 2018-12-31 01:05

var items = Array("elm1","elm2","elm3","elm4",...);

var item = items[Math.floor(Math.random()*items.length)];

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Getting a random value from a JavaScript array

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