shuffle array elements
I found this code online for shuffling array elements, it works well, but I can't understand the for loop here
shuffle = function(o)
{
for(var j, x, i = o.length; i;
j = parseInt(Math.random() * i), x = o[--i], o[i] = o[j], o[j] = x);
return o;
};
any help is appreciate开发者_Go百科d, thank you !
This is basically a misuse of the flexibility of the for loop.
The general syntax for a for loop is:
for (<init>; <condition>; <increment>) {
<body>
}
which roughly can be expressed as following while loop:
<init>;
while(<condition>) {
<body>
<increment>
}
Since both <body> and <increment> are both executed as if they were in the body of the while, anything that can go into the body of a for loop, can also be put in the <increment> expression of the for loop. You just have to separate the statements with commas instead of semicolons.
Thus your for loop is probably better expressed as following while loop:
var j, x, i = o.length;
while (i) { // same as while(i != 0)
j = parseInt(Math.random() * i);
x = o[--i];
o[i] = o[j];
o[j] = x;
}
j = parseInt(Math.random() * i); // Getting a random number between 0 to n-1, where n is the length of the array.
x = o[--i]; // Getting the last element of the array and storing it in a variable.
o[i] = o[j]; // Storing the randomly selected index value at the last position.
o[j] = x; // Storing the last element's value in random position.
i value will decrement in each loop iteration and it will replace the last then next to last then so on... and finallly first element of the array with a random element within the aray.
加载中,请稍侯......
精彩评论