Question

i am using a class to make some calculations with matrices, in this case: Get the sum of each column.

The sum output is correct, and if I hide the notices, the problem is solved, but logically, i prefer the correction.

In PHP 5.3 I get some notices in this function:

Notice: Undefined offset: 0 
Notice: Undefined offset: 0 
Notice: Undefined offset: 1 

script

function sum()
    {
        foreach($this->numbers as $i => $rows)
        {
            foreach($rows as $j => $number)
            {
                $this->sum[0][$j] += $number; //notices here
            }
        }
        $the_sum = new matrix($this->sum, 1, $this->get_num_columns());

        return $the_sum;
    }

Matrix:

1     | 4

0.25  | 1



var_dump($this->numbers);
array
  0 => 
    array
      0 => int 1
      1 => float 4
  1 => 
    array
      0 => float 0.25
      1 => int 1

and

 $this->get_num_columns() // 2

Any idea to correct these notices ?

thanks

Answer 1

Yes, the notice occurs because there is no initial value in the variables you are adding numbers to. You should check if the number exists and initialize it before you add a number to it. (Note, this won’t improve your result, but it is good practice to initialize variables).

function sum()
    {
        foreach($this->numbers as $i => $rows)
        {
            foreach($rows as $j => $number)
            {
                if (!isset($this->sum[0][$j])) $this->sum[0][$j] = 0;
                $this->sum[0][$j] += $number; //no notices here
            }
        }
        $the_sum = new matrix($this->sum, 1, $this->get_num_columns());

        return $the_sum;
    }

---

Unrelated Points to Consider

• Proper naming standards dictate that class name should be capitalized, to differentiate them from functions. So you should name your class Matrix and not matrix.
• If you get the chance, a much better solution would be to pre-fill your array with 0s. array_fill() does the job nicely.