I was fed up with the limited javascript Array functions and wanted to write a few of my own handy prototype functions to perform Set Theory functions.
Below is the code I have for this so far
<script type="text/javascript">
Array.prototype.contains = function(obj) {
var i = this.length;
while (i--) {
if (this[i] === obj) {
return true;
}
}
return false;
}
Array.prototype.getIndices = function(obj){
var indices = new Array();
var i = this.length;
while (i--) {
if(this[i] === obj){
indices.push(i);
}
}
return indices;
}
Array.prototype.Union = function(arr){
//combines two arrays together to return a single array containing all elements (once)
//{1,2,3,4,5}.Union({3,4,5,6,7})
//returns: {1,2,3,4,5,6,7}
var primArray = this;
var secondArray = arr;
var i = primArray.length;
while(i--){
if(secondArray.contains(primArray[i])){
primArray.splice(i, 1);
}
}
var returnArr = primArray.concat(secondArray);
return returnArr;
}
Array.prototype.Intersection = function(arr){
//Returns an array of elements that are present in both sets
//{1,2,3,4,5}.Intersection({3,4,5,6,7})
//returns: {3,4,5}
var primArray = this;
var secondArray = arr;
var returnArr = new Array;
var i = 0;
while(i++<primArray.length){
if(secondArray.contains(primArray[i])){
returnArr.push(primArray[i]);
}
}
return returnArr;
}
Array.prototype.Complement = function(arr){
//Returns an array of elements that are only in the primary (calling) element
//{1,2,3,4,5}.Complement({3,4,5,6,7})
//return: {1,2}
var primArray = this;
var secondArray = arr;
var i = primArray.length;
while(i--){
if(secondArray.contains(primArray[i])){
primArray.splice(i, 1);
}
}
return primArray;
}
Array.prototype.SymmetricDifference = function(arr){
//Returns elements that are exclusive to each set
//{1,2,3,4,5}.SymmetricDifference({3,4,5,6,7})
//return: {1,2,6,7}
var primArray = this;
var secondArray = arr;
var i = primArray.length;
while(i--){
if(secondArray.contains(primArray[i])){
var indices = secondArray.getIndices(primArray[i]);
primArray.splice(i, 1);
var j=indices.length;
while(j--){
secondArray.splice(indices[j], 1);
}
}
}
var returnArr = primArray.concat(arr);
return returnArr;
}
function run(){
var Q = "A";
var D = [1,2,3,4,5,6,7,8,9,10];
var sets = {
"A":[1,2,3],
"B":[3,4,5],
"C":[5,6,7]
}
var R = D;
for(var el in sets){
R = R.Complement(sets[el]);
}
//if I alert D at this point I get 8,9,10 instead of 1,2,3,4,5,6,7,8,9,10 as I would expect? What am I missing here... It causes a problem when I perform D.Complement(R) later on
document.write(R + "<br/>");
R = R.Union(sets[Q]);
document.write(R + "<br/>");
//Here!
R = D.Complement(R);
document.write(R);
}
</script>
</head>
<body onload="run()">
</body>
</html>
Everything is working up to the final point when I then try to get the complement of the domain and my newly constructed set. I am expected to be getting the complement of [1,2,3,4,5,6,7,8,9,10] and [8,9,10,1,2,3] which would yield [4,5,6,7] but when I perform D.Complement(R) my D variable seems to have turned into [1,2,3]. This appears to happen after the enumeration I perform.
I thought it might be because I was using this.splice and arr.splice in my functions and when I was passing the variables to the functions they were being passed as pointers meaning I was actually working on the actual memory locations. So I then used primArray and secondArray to create a duplicate to work on… but the problem is still happening
Many Thanks
Just assigning it to a variable does not make it a new array, you are still working on the array that was passed in. You have to manually make a new copy of the array either by looping through it and copy each index or by joining and splitting.