2 random images but not the same one

I have this function that shows two random images picked from a folder. Is there any chance I can modify the code so that I won't have the same image twice as result?

Thanks in advance.

var theImages = new Array()

theImages[0] = 'img/dyptichs/f-1.jpg'
theImages[1] = 'img/dyptichs/f-2.jpg'
theImages[2] = 'img/dyptichs/f-3.jpg'
theImages[3] = 'img/dyptichs/f-4.jpg'
theImages[4] = 'img/dyptichs/f-5.jpg'

var j = 0
var p = theImages.length;
var preBuffer = new Array()
for (i = 0; i < p; i++){
preBuffer[i] = new Image()
preBuffer[i].src = theImages[i]
}
var WI1 = Math.round(Math.random()*(p-1));
var WI2 = Math.round(Math.random()*(p-2));

function showImage1(){
document.write('<img src="'+theImages[WI1]+'">');
}
function showImage2(){
document.write('<img src="'+theImages[WI2]+'">');
}


3 Answers
3

You can do something like this:

var WI1 = Math.round(Math.random()*(p-1));
var WI2 = Math.round(Math.random()*(p-1));
while (WI2 === WI1) {
WI2 = Math.round(Math.random()*(p-1));
}


We keep generating a new number until it's different from WI1, ensuring it is unique.

The way I'd personally handle that is to randomise the array and then just grab the first 2 entries. That way you still pick 2 at random, but you guarantee not to get the same 2.

var theImages = new Array()

theImages[0] = 'img/dyptichs/f-1.jpg'
theImages[1] = 'img/dyptichs/f-2.jpg'
theImages[2] = 'img/dyptichs/f-3.jpg'
theImages[3] = 'img/dyptichs/f-4.jpg'
theImages[4] = 'img/dyptichs/f-5.jpg'

var randomImages = theImages
.concat()
.sort(function () {

return Math.random() > 0.5
? 1
: -1;

})
.slice(0, 2);

function showImage1() {
document.write('<img src="' + randomImages[0] + '">');
}

function showImage2() {
document.write('<img src="' + randomImages[1] + '">');
}


Edit: including the original array for a complete solution

randomImages

var WI1 = Math.floor(Math.random()*p);
var WI2 = Math.floor(Math.random()*(p-1));
if (WI2 >= WI1) {
WI2 += 1;
}


Use floor instead of round and subtract 1, because with round you get twice less chance to get first or last element.

The if trick is slightly better than a loop in this case, though the loop is easier to apply to a more complex case.

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