PHP comparing values with a for loop in arrays gives an offset error

Question

I have 2D arrays where I have to keep comparing the next value. I am using a for loop to go through all values and I am getting an offset error because when it reaches the last array, it wants to check the next array, which does not exist. How can I prevent that? I know that ($items[$row][0]!=$items[$row+1][0]) is the issue. Should I not use a for loop?

What I do not understand is that the code below does not give any error. If $items[$row+1][0] is the problem when it reaches the last array, shouldn't $items[$row-1][0] give an error as well when it is checking the first array in the arrays?

if ($row==0 || ($row>0 && $items[$row][0]!=$items[$row-1][0]) )

But this one is not ok.

Notice: Trying to access array offset on value of type null
Notice: Undefined offset

        if (($row<$num_rows && ($items[$row][0]!=$items[$row+1][0]))||$num_rows==$is_odd)  {
        //$is_odd is the number of last array.  
        //$num_rows is the total number of arrays. 
        echo "</table></div></div>";

    }

Clearly, you should compare the array only up to the next-to-last element, and no further. Your first example explicitly checks that $row is not zero, so $row-1 always exists. — LSerni
– LSerni, Commented May 27, 2020 at 14:50
As a quick fix, you can use the null coalesce operator ?? - $items[$row+1][0] ?? -1 (the -1 would be some dummy value which you can set to something appropriate for your case). — Nigel Ren
– Nigel Ren, Commented May 27, 2020 at 15:38

Shamim Shaikh · Accepted Answer · 2020-05-27 15:06:17Z

1

in your condition check next index is exist or not like

if ((!empty($items[$row + 1]) && $row < $num_rows && ($items[$row][0] != $items[$row + 1][0])) || $num_rows == $is_odd) {
    //$is_odd is the number of last array.  
    //$num_rows is the total number of arrays. 
    echo "</table></div></div>";
}

answered May 27, 2020 at 15:06

Shamim Shaikh

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1 Comment

Kei Moon Over a year ago

Thank you. I didn't know that empty can check the index. It worked. Can't believe I struggled for a couple of days for this...

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