Question

I’m doing this project trying to reproduce Schelling’s Segregation model. I have a function(below) that is testing to see if the four immediate adjacent cells of the array are either the same or different or empty compared to the current cell being tested.

There are four possible spots to be tested for every cell in the array. But on corners and side spots, obviously you cant test spaces that are out of bounds. So in the function, if it finds one of the out of bounds spaces it decrements the number total around the cell. However, it keeps crashing telling me that I have an Uncaught Reference Error: Cannot read property ‘0’ of undefined. I can’t tell why its crashing.

The final lines of this code take the number of goods(similar cells) and the total number of cells around it (empty cells do not count) and gets a percentage similar.

Any help would be appreciated into telling me why it might be crashing and giving me an error? Thanks!

model.Test = function( i, j )
{
var numberToTest= 4;
var goods= 0;

if ((i - 1) >= 0) 
{
    if (model.BoardArray[i-1][j] != "E")
    {
        if (model.BoardArray[i][j] == model.BoardArray[i-1][j])
        {
            goods++;
        }
    }
    else
    {
        numberToTest--;
    }
}
else
{
    numberToTest--;
}


if((i + 1) < $("#BoardSizeValue").val()) 
{
    if (model.BoardArray[i+1][j] != "E")
    {   
        if (model.BoardArray[i][j] == model.BoardArray[i+1][j])
        {
            goods++;
        }
    }
    else
    {
        numberToTest--;
    }
}
else
{
    numberToTest--;
}


if ((j - 1) >= 0) 
{
    if (model.BoardArray[i][j-1] != "E")
    {
        if (model.BoardArray[i][j] == model.BoardArray[i][j-1])
        {
        goods++;
        }
    }
    else
    {
        numberToTest--;
    }
}
else
{
    numberToTest--;
}


if ((j + 1) < $("#BoardSizeValue").val()) 
{
    if (model.BoardArray[i][j+1] != "E")
    {   
        if (model.BoardArray[i][j] == model.BoardArray[i][j+1])
        {
            goods++;
        }
    }
    else
    {
        numberToTest--;
    }
}
else
{
    numberToTest--;
}


var similar = $("#SimilarSlider").val()/100;
if (numberToTest == 0)
{
    return false;
}
else
{
    var needed = goods/numberToTest;

    if (needed >= similar)
    {
        return false;
    }
    else
    {
        return true;
    }
}
}

Answer 1

From looking at your code, you would only get a Reference Error: Cannot read property '0' of undefined. if i was out of the bounds of the array.

I think the problem might be in this part of the code:

if ((i - 1) >= 0) {
    if (model.BoardArray[i-1][j] != "E") {
        if (model.BoardArray[i][j] == model.BoardArray[i-1][j]) {

if i = $("#BoardSizeValue").val() and $("#BoardSizeValue").val() is a one-based index of the array size, then [i-1] would be okay, but not [i]. So try adjusting your code to this:

if ((i - 1) >= 0 && i < $("#BoardSizeValue").val()) {
    if (model.BoardArray[i-1][j] != "E") {
        if (model.BoardArray[i][j] == model.BoardArray[i-1][j]) {

This would also apply to the j comparisons as well.