array.splice not working correctly in javascript

Question

I'm writing a simple sudoku solver, which takes an array of numbers 1-9 and sets them to null if they are not possible for that cell. An example is a cell where the answer can only be a 5, so all the numbers are set to null except for five. Then, I have a clean() function which deletes all the values from the array which are null, but that is not working correctly. The original array is this.

[null,null,null,null,5,null,null,null,null]

After being cleaned, it returns

[null,null,5,null,null]

The javascript code is here, and the grid is the grid of numbers in the sudoku

function mainmethod(){

        var onepos=oneposs();

    }
    function oneposs(){

        var possibs=new Array(1,2,3,4,5,6,7,8,9);
        for (var ycount=0;ycount<=8;ycount++){
            var value=grid[0][ycount];
            var index=possibs.indexOf(value);
            possibs[index]=null;

        }
    //      for(var xcount=0;xcount<=8;xcount++){
    //      var value=grid[xcount][0];
    //      var index=possibs.indexOf(value);
    //      possibs.splice(index,1);
    //  }

        possibs=clean(possibs);
        alert(JSON.stringify(possibs));
    }
    function clean(array){
        for(var i=0;i<=8;i++){
            if(array[i]===null){
                array.splice(i,1);
            }
        }
        return array;
    }

Essentially, the array.splice is not splicing everything it needs to, and I don't know why

Bali Balo · Accepted Answer · 2013-03-16 23:33:45Z

6

You change the array while you iterate. Try something like that:

function clean(array){
    for(var i=0;i<=8;i++){
        if(array[i]===null){
            array.splice(i--,1);
        }
    }
    return array;
}

The -- lower the index because the next item will then be at the same index than the item you are removing.

Moreover, objects and arrays passed as argument are passed by reference so you don't need to return anything. You can do clean(possibs);

answered Mar 16, 2013 at 23:33

Bali Balo

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Comments

Daniel Flores · Accepted Answer · 2013-03-16 23:31:59Z

2

That's because when you "splice" the array , the index change. Maybe you can try this code :

function clean(array){
    var x = [];
    for(var i=0;i<array.length;i++){
        if(array[i]!=null){
            x.push(array[i]);
        }
    }
    return x;
}

answered Mar 16, 2013 at 23:31

Daniel Flores

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Comments

hnafar · Accepted Answer · 2013-03-16 23:50:50Z

1

try this:

var array = [null,null,null,null,5,null,null,null,null];
for(var i=0;i<=array.length; ){
    if(array[i] === null){
        array.splice(i,1);
    } else if (array.length < 2) {
        break;
    } else {
        i++;
    }
}

answered Mar 16, 2013 at 23:50

hnafar

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