I think one idea is to make a new array with only the randomizable things, shuffle it, and then place them back into the old array. Check this out:
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-js -->
var array = [
{
randomize: true,
value: 'value_1'
},
{
randomize: false,
value: 'value_2'
},
{
randomize: false,
value: 'value_3'
},
{
randomize: true,
value: 'value_4'
},
{
randomize: false,
value: 'value_5'
},
{
randomize: true,
value: 'value_6'
},
{
randomize: true,
value: 'value_7'
},
];
// https://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array
function shuffle(array) {
var currentIndex = array.length, temporaryValue, randomIndex;
// While there remain elements to shuffle...
while (0 !== currentIndex) {
// Pick a remaining element...
randomIndex = Math.floor(Math.random() * currentIndex);
currentIndex -= 1;
// And swap it with the current element.
temporaryValue = array[currentIndex];
array[currentIndex] = array[randomIndex];
array[randomIndex] = temporaryValue;
}
return array;
}
// make a list of all randomizable elements
var randomizable = array.filter(o => o.randomize);
// shuffle their order
shuffle(randomizable);
// to make this easy to reason about, i think i'll make all the randomizeable elements in the first array null
array.forEach(function(el, index) {
if (el.randomize) array[index] = null;
});
console.log(array);
// now, we can iterate over the null slots and place in elements from randomizable
array.forEach(function(el, index) {
if (el === null) {
array[index] = randomizable.pop();
}
});
console.log(array);
<!-- end snippet -->
The de-facto unbiased shuffle algorithm is the Fisher-Yates (aka Knuth) Shuffle.
See https://github.com/coolaj86/knuth-shuffle
You can see a [great visualization here][0] (and the original post [linked to this][1])
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-js -->
function shuffle(array) {
var currentIndex = array.length, temporaryValue, randomIndex;
// While there remain elements to shuffle...
while (0 !== currentIndex) {
// Pick a remaining element...
randomIndex = Math.floor(Math.random() * currentIndex);
currentIndex -= 1;
// And swap it with the current element.
temporaryValue = array[currentIndex];
array[currentIndex] = array[randomIndex];
array[randomIndex] = temporaryValue;
}
return array;
}
// Used like so
var arr = [2, 11, 37, 42];
shuffle(arr);
console.log(arr);
<!-- end snippet -->
Some more info [about the algorithm][2] used.
[0]: http://bost.ocks.org/mike/shuffle/
[1]: http://sedition.com/perl/javascript-fy.html
[2]: http://en.wikipedia.org/wiki/Fisher-Yates_shuffle
