Remove duplicate entries from array of arrays (javascript)

Question

I am trying to use javascript to remove duplicate entries in an array of arrays in which the duplicates will always be in an array of length 1. An example would be

[  [23, 46, 43, 44]
   [46]
   [52, 51]       
   [53]
   [44]
   [55, 66] ]

In this case I would want to remove the arrays [46] and [44], but leave [53]. The number of these single entry duplicate arrays is variable. Ideas?

Edit: Here's what I ended up doing that worked where stacks_array is the array of arrays.

function stacks_sanatizer(stacks_array){

    var output_array = [],      
    used_cards =[];
    used_cards[70] = undefined;     

    for (each_stak in stacks_array){
        if((stacks_array[each_stak].length > 1) && (stacks_array[each_stak] !== "")){
            for (i=0; i<stacks_array[each_stak].length;i++){
                var card_number = stacks_array[each_stak][i].attrs.fill.substr(27).replace('.jpg)','');
                used_cards[card_number - 1] = true;
            }
        }
    }

    for (each_stak in stacks_array){
        if(stacks_array[each_stak] !== ""){
            if(stacks_array[each_stak].length === 1){
                card_number = stacks_array[each_stak][0].attrs.fill.substr(27).replace('.jpg)','');
                if(used_cards[card_number - 1] !== true){
                    output_array.push(stacks_array[each_stak]);
                    used_cards[card_number - 1] = true;
                }
            }
            else{
                output_array.push(stacks_array[each_stak]);
            }
        }
    }

    //delete doubles    
    for(each_pile in output_array){ 
        output_array[each_pile] = output_array[each_pile].filter(function(elem, pos) {
            return output_array[each_pile].indexOf(elem) == pos;
        })  
    }
    return output_array;
}

hashtables...alway hashtables. Well like 99% of the time it's hashtables. In addition check if the element came from an array of length 1. — Ben
– Ben, Commented Jul 11, 2014 at 21:06
Can the single array to remove come before the duplicate entry in the longer array? — Teepeemm
– Teepeemm, Commented Jul 11, 2014 at 21:20
@Teepeemm oh that's a good question. To modify my comment a bit, you could iterate through the outer list twice, hashing inner lists of len > 1 the first time, and on the second time around, check for dupes — Ben
– Ben, Commented Jul 11, 2014 at 21:22
Please show what you've tried. We're not here to do your work for you, we'll help you fix problems in your code. — Barmar
– Barmar, Commented Jul 11, 2014 at 21:27

Hongyi Li · Accepted Answer · 2014-07-11 21:39:43Z

1

Pseudocode to accomplish this:

Iterate through the outer array: for each inner array, hash the number into a hash table.
While you hash it into the table, if there is an existing entry for it, check if the length of that array is 1, and if yes remove the array.
Otherwise, enter the entry into the hash table and leave that inner array be.

Hope this helps :)

answered Jul 11, 2014 at 21:39

Hongyi Li

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Justin Jasmann · Accepted Answer · 2014-07-11 21:35:27Z

1

You would probably want to use some combination of a hash to lookup collisions and then splice what you don't want out.

Like so:

function removeDuplicates(listOfLists) {
    var hash = {};
    for (var i = 0; i < listOfLists.length; i++) {
        var array = listOfLists[i];
        for (var j = 0; j < array.length; j++) {
            var val = array[j];
            var hashedVal = hash[val];
            if (hashedVal === undefined) {
                hash[val] = true;
            }
            else {
                array.splice(j, 1);
                if (array.length === 0) {
                    listOfLists.splice(i, 1);
                }
            }
        }
    }
}

answered Jul 11, 2014 at 21:35

Justin Jasmann

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