Group elements based on values

JSON:

var obj = {
    'itemA' : {
        'x' : '300',
        'y' : '200'
    },
    'itemB' : {
        'x' : '305',
        'y' : '210'
    },
   'itemC' : {
        'x' : '442',
        'y' : '210'
    }
};

What I need to do is pick up these items and instead of displaying the 3, display only groups that group the items next to each other. For example, the x and y of the itemA and itemB are nearby so instead of displaying 2, it would only display 1 grouping. Since the itemC has the x far away and the y near, but since it has to be x and y that has to be close, then it would display it without grouping with the others would display 2 items on the screen.

I'm still not sure how to do this with Javascript or jQuery , and even PHP if that's the case, but I'd like it in JS / jQuery.