distinct array

distinct array

hey guys...im trying to get a list of all categoryies from an array (below).

the result im trying to get is:
Footwear, Clothes

but not:
Footwear, Clothes, Footwear, Clothes

the array below could contain 100's or even 1000's of items so a foreach loop would be too slow to get the categories feature in the array.

is there a easy solution to get the results im after please...thank you

  1. var items = [{
        "title": "Nike air MAX",
            "distance": "5 Miles",
            "end_timestamp": "2010-12-15 21:51:45",
            "total_price": "18.00",
            "condition": "Used",
            "category": "Footwear",
            "sub-category": "Trainers",
            "location": "Middle East",
            "buy_now" : "0"
    }, {
        "title": "Levis Jeans",
            "distance": "5 Miles",
            "end_timestamp": "2010-12-15 21:51:45",
            "total_price": "38.00",
            "condition": "New",
            "category": "Clothes",
            "sub-category": "Jeans",
            "location": "United Kindgom",
            "buy_now" : "1"
    }, {
        "title": "Gola Cheap Trainers",
            "distance": "4 Miles",
            "end_timestamp": "2012-11-15 21:51:45",
            "total_price": "99.99",
            "condition": "Broken",
            "category": "Footwear",
            "sub-category": "Trainers",
            "location": "Europe",
            "buy_now" : "0"
    }, {
        "title": "Desil Shirt",
            "distance": "7 Miles",
            "end_timestamp": "2000-12-15 21:51:45",
            "total_price": "50.00",
            "condition": "Used",
            "category": "Clothes",
            "sub-category": "Shirts",
            "location": "Europe",
            "buy_now" : "1"
    }];