numberArray.sort(function(){..} - DallasNYC

this is where i first came across the "harlem shuffle" -
http://groups.google.com/group/macro...b71816b688db0f
for a fuller explanation, try googling for years as i have done ( if you ever find one, let me know :thumbsup: ) or try to make sense of trace outs -

Code:

---

arr1=[1,2,3,4,5,6];;
arr2 = [1,2,3,4,5,6,7,8,9];

function shuffle(){
nVal = Math.floor(Math.random()*3)-1;
return nVal;
};

chk = 0;

function tracer(){
++chk>arr2.length ? clearInterval(traceInt) : null;
num = Math.floor(Math.random()*3)-1;
arr1.sort(num);
trace("num = "+num+" returns - "+arr1);
arr2.sort(shuffle);
trace("nVal = "+nVal+" returns - "+arr2);
}

traceInt = setInterval(tracer,50);

---

Thanks Dog, I'm slowly understanding it, but not 100%.

From flash help:

Quote:

---

public sort([compareFunction:Object], [options:Number]) : Array

---

My first mistake was thinking that just by putting a number (-1, 0,or 1)for the parameter would give the same result.

Code:

---

myArray.sort(-1)

---

However, this will only result in sending the second '[options:number]' parameter. Probally defaults to 1, since -1 and 0 are not options.

For the three numbers (1, 0, -1) to work, we must use a function as the first parameter.
Then by adding a trace within that function, you will see that the sort method actaully calls on the function several times..

Code:

---

numberArray = [];
for (var n = 0; n != 4; n++) {//using only 4 to reduce the possible results
        numberArray.push(n);
}
trace("original = "+numberArray);
randNum = function () {
        nVal = Math.floor(Math.random()*3)-1;
        trace(nVal);
        return nVal;
};
numberArray.sort(randNum);
trace("random = "+numberArray);

---

traces out..

Quote:

---

original = 0,1,2,3
1
-1
-1
1
1
random = 1,2,0,3

---

The amount of times the sort method calls the function varies depending on the previous comparison. Since the sort method sends two values to the function, we can trace them out to get a better idea of what is going on..

Code:

---

numberArray = [];
for (var n = 0; n != 4; n++) {
        numberArray.push(n);
}
trace("original = "+numberArray);
randNum = function (a, b) {
        trace("-------------");
        trace("comparing: "+a+":"+b);
        nVal = Math.floor(Math.random()*3)-1;
        trace("using: "+nVal);
        return nVal;
};
numberArray.sort(randNum);
trace("random = "+numberArray);

---

At this point, I'm still not clear how the sort method picks which two items in the array to compare. But I'm atleast to the point that I understand that we are telling flash to use a random comparison for each pair.

Thanks..

Actaully, we dont need to use -1,0,1. We can return any positive or any negative. This works well for sorting numbers correctly. If we use sort() without any parameters, we get a wacky list, because flash puts '10' before '2'. But if we use our own function, we can use some simple math to let flash know the right order..

Code:

---

numberArray = [];
for (var n = 0; n != 20; n++) {
        numberArray.push(n);
}
trace("original = "+numberArray);
randNum = function (a, b, c) {
        nVal = Math.floor(Math.random()*3)-1;
        return nVal;
};
numberArray.sort(randNum);
trace("random = "+numberArray);
numberArray.sort();
trace("In order? = "+numberArray);
sortAscending = function (a, b) {
        return a-b;
};
numberArray.sort(sortAscending);
trace("Really in Order = "+numberArray);

---

O.K. so now sort(function) is really coming together for me..

Glad to hear it's coming together :thumbsup:

I still don't fully understand it, but your explanation throws some light on the internal workings :D