Question

Using JavaScript, I’d like to split one big array of coordinates into smaller arrays based on coinciding points. I am not 100% sure how to write the following in code but it describes what I’m attempting to achieve:

1. Iterate through the array

   var A = [(1,2)(1,3)(2,3)(9,10)(9,11)(10,11)];

2. Combine the pairs that contain any matching/identical coordinate points:

   var B = (1,2)(1,3)(2,3)

   var C = (9,10)(9,11)(10,11)

3. Combine the matching/identical points and create new, smaller arrays from the combinations in point #2

   var D = [1,2,3]

   var E = [9,10,11]

Can I get help please?

Answer 1

Working answer: http://jsfiddle.net/y3h9L/

OK, so if I understand the requirement A is a one-dimensional array that is assumed to have an even number of elements in x,y pairs.

A = [1,2,  1,3,  2,3,  9,10,  9,11,  10,11]
// output should be
[ [1,2,3], [9,10,11] ]

// but if you add an extra pair that links the two halves, say add 2,11
A2 = [1,2,  1,3,  2,3,  9,10,  9,11,  10,11,   2,11]
// then all are related so output should be
[ [1,2,3,9,10,11] ]

I’ve made no effort to pretty-up or optimise the following code, but it works:

// single dimensional array of x,y pairs
var A = [1,2,  1,3,  2,3,  9,10,  9,11,  10,11];

// create a working copy of A so that we can remove elements
// and still keep the original A intact.
var workingCopy = A.slice(0, A.length),
    matchedPairs = [],
    currentMatches,
    finalCombinations = [],
    x, y, i, j,
    tempArray;

while (workingCopy.length > 0) {
   currentMatches = [];
   currentMatches.push([workingCopy.shift(),workingCopy.shift()]);

   workingCopyLoop:
   for (x=0,y=1; x < workingCopy.length;) {
      for (i=0; i < currentMatches.length; i++){
         if (workingCopy[x] === currentMatches[i][0]
            || workingCopy[y] === currentMatches[i][1]) {
            currentMatches.push([workingCopy.shift(),workingCopy.shift()]);
            // go back to the beginning of workingCopyLoop
            x=0;
            y=1;
            continue workingCopyLoop;
         }
      }

      x += 2;
      y += 2;
   }   

   matchedPairs.push(currentMatches);
}

for (i=0; i<matchedPairs.length; i++){
   tempArray = [];
   for (j=0; j<matchedPairs[i].length; j++) {
      // I assume you have a new enough version of JS that you have Array.indexOf()
      if (-1 === tempArray.indexOf(matchedPairs[i][j][0]))
         tempArray.push(matchedPairs[i][j][0]);
      if (-1 === tempArray.indexOf(matchedPairs[i][j][1]))
         tempArray.push(matchedPairs[i][j][1]);
   }
   finalCombinations.push(tempArray);
}

for (i=0; i<finalCombinations.length; i++)
   console.log(finalCombinations[i]);

// console.log shows that finalCombinations = [ [1,2,3], [9,10,11] ]

If it’s not obvious how this works, follow it through with a debugger and/or pencil and paper.