Fill two-dimensional array per row

Question

I have a function (getCoeff()) which returns one-dimensional arrays. I try to use it to fill a two-dimensional array:

//set up an 3x3 array for A
A = new Array(3);
for (var i=0; i<3; i++) {
    A[i] = new Array(3);
}

//fill it per row using getCoeff()
for (var i=0; i<3; i++) {
        A[i] = getCoeff(i+1);
}

console.log(A);
console.log(getCoeff(1));
console.log(getCoeff(2));
console.log(getCoeff(3));

but I only get the first row filled and the other two remain empty:

[ [ -3, 2, -1 ], [ , ,  ], [ , ,  ] ]
[ -3, 2, -1 ]
[ 2, -3, 2 ]
[ 1, -1, 3 ]

As you can see the function returns the rows correctly but for some reason It doesnt work inside the loop.

On the other hand if I try something like this:

for (var i=0; i<3; i++) {
        A[i] = [1,2,3];
}
console.log(A);

it works fine!

[ [ 1, 2, 3 ], [ 1, 2, 3 ], [ 1, 2, 3 ] ]

What's wrong with my code?!

Update:

My original full code before the edits:

    var fs = require('fs');
    var input = "LPinput.txt";
    var c = new Array();
    var A = new Array();
    var b = new Array();
    var Eqin = new Array();
    var MinMax;

    open(input);

    console.log(c);
    console.log(A);
    console.log(b);
    console.log(Eqin);
    console.log(MinMax);

    function open(filename) {
        if (fs.existsSync(filename)) {
           var data = fs.readFileSync(filename).toString().split("\n");
           analyse(data);
        } else {
           console.log("ERROR: File doesnt exist!");
        }
    }

    function analyse(data) {

        //clean up whitespaces
        for (i in data) {
            data[i] = data[i].replace(/\s/g, '');       
        }   

        //check LP type & clean up
        if (data[0].substring(0,3) == "max") {
            MinMax = 1;
            data[0] = data[0].replace("max","");
        } else if (data[0].substring(0,3) == "min") {
            MinMax = -1;
            data[0] = data[0].replace("min","");
        } else {
            console.log("ERROR: Invalid format!");
            return;
        }

        //check constraints format & clean up
        if ( data[1].substring(0,4) != "s.t.") {
            console.log("ERROR: Invalid format!");
            return;
        } else {
            data[1] = data[1].replace("s.t.","");
        }

        //get variables 
        var variables = data[data.length-1].split(",");
        var last = variables[variables.length-1];
        variables[variables.length-1] = last.substring(0,last.indexOf(">"));

        //get number of constraints
        var constraints = data.length-2;

        c = getCoeff(0);

            //===============================
            //I JUST NEED TO POPULATE A TO FINISH THIS
        for (var i=0; i<constraints; i++) {
            A[i] = getCoeff(i+1);
        }   
            //===============================

        for (var i=1; i<data.length-1; i++) {
            var end = data[i].length;
            var start = end;
            while (data[i].charAt(start) != "=") {
                 start = start - 1;
            }
            b[i-1] = parseInt(data[i].substring(start+1,end));

            if (data[i].charAt(start-1) == "<") {
                Eqin[i-1]=-1;
            } else if (data[i].charAt(start-1) == ">") {
                Eqin[i-1]=1;
            } else {
                Eqin[i-1]=0;
            }

        }

        function getCoeff(row) {
            var coeff = new Array();
            for (i in variables) {
                var pos = data[row].indexOf(variables[i]);
                if ((data[row].charAt(pos-1) == "+") || (pos-1 < 0)) {
                    coeff[i]=1;
                } else if (data[row].charAt(pos-1) == "-") {
                    coeff[i]=-1;
                } else if (data[row].charAt(pos-1) == "*") {
                    var end = pos-1;
                    var start = end;
                    while ( (start > -1) && (data[row].charAt(start) != "+") && (data[row].charAt(start) != "-") ) {
                        start = start - 1;
                    }
                    coeff[i] = parseInt((data[row].substring(start,end)));
                }
            }
            return coeff;
        }

    }

LPinput.txt:

max 2*x1+x2-4*x3-15
s.t.-3*x1+2*x2-x3>=5
    2*x1-3*x2+2*x3<=9
    x1-x2+3*x3<=5
    x1,x2,x3>=0

Update #2:

Console output:

[ 2, 1, -4 ]
[ [ -3, 2, -1 ] ]
[ 5, 9, 5 ]
[ 1, -1, -1 ]
1

It should be:

[ 2, 1, -4 ]
[ [ -3, 2, -1 ],[ 2, -3, 2 ],[ 1, -1, 3 ]]
[ 5, 9, 5 ]
[ 1, -1, -1 ]
1

Answer 1

Here is the real problem: you are using an i variable in your outer scope.

    for (var i=0; i<constraints; i++) {
        A[i] = getCoeff(i+1);
    }   

When you go inside the getCoef you have this for loop

for (i in variables) {

and since you have not declared the i here, it uses the same i declared in the outer scope. After the first run of the for loop (which fills the first row of A), i is changed to "0" as opposed to the numeric value 0. Therefore the condition of the for loop is no longer valid and it exits the loop.

There you go!

Answer 2

In your code:

A = new Array(3);

you should declare varaibles, and initialising an array with a length is usually unnecessary. Also, variables starting with a capital letter are, by convention, reserved for construtors (though some use variable names in all capitals to represent constants).

Consider using an array initialiser:

var a = [];   
for (var i=0; i<3; i++) {

Initialising arrays in the following loop is a bit useless as you replace them in the next loop:

    a[i] = [];
}

In the next loop, i is needlessly declared again (there is no block scope in javascript). It is common to use a different variable in these cases (though re-using i has no ill effects, it's just not liked):

for (var j=0; j<3; j++) {
        a[j] = getCoeff(j + 1);
}

So creating a getCoeff function that just returns an array of the value passed to it (purely for testing):

function getCoeff(v){
  return [v,v,v]; 
} 

"works":

console.log(a.join(' - ')); // 1,1,1 - 2,2,2 - 3,3,3

Answer 3

In my case, I got last 2 populated. Anyways, if you run loop from 0, you better write

A[i] = getCoeff(i+1);

OR

you run that loop starting from 1 to less than equals 3.