How to sum identical elements in a 2D array in PHP

In PHP, a two-dimensional array is a very common data structure. It consists of multiple one-dimensional arrays and stores relatively complex data structures. When it comes to the operation of two-dimensional arrays, sometimes it is necessary to sum the same elements. In this article, we will share how to sum identical elements in a two-dimensional array in PHP.

First of all, we need to understand what a two-dimensional array is. A two-dimensional array is an array in which each element is an array. We can define a two-dimensional array in the following way:

$array = array(
  array(1, 2, 3),
  array(4, 5, 6),
  array(7, 8, 9)
);

Here we define a 3x3 two-dimensional array. Among them, each sub-array has the same number of elements and is arranged in a certain order. Next, we'll learn how to sum identical elements in these subarrays.

The first method is to use a foreach loop. We can iterate through each sub-array in the 2D array and use another foreach loop to iterate over each element in the sub-array and finally sum all the same elements. The implementation code is as follows:

$sums = array();

foreach ($array as $subarray) {
  foreach ($subarray as $key => $value) {
    if (isset($sums[$key])) {
      $sums[$key] += $value;
    }
    else {
      $sums[$key] = $value;
    }
  }
}

print_r($sums);

In this code, we first create a new array named $sums. We use a double loop to iterate through each sub-array in the 2D array and each element in each sub-array. For each element, we check if it already exists in $sums. If so, add the original value to the element; if not, add the value to $sums. Finally, we print $sums to see the results.

The second method is to use the array_reduce function. This function takes each element in the array as a parameter and returns a cumulative value. We can use the array merge operator " " to merge all the arrays into one array and use the array_reduce function to sum the elements with the same key. The implementation code is as follows:

$sums = array_reduce($array, function ($result, $subarray) {
  return $result + $subarray;
}, array());

print_r($sums);

In this code, we use the array_reduce function to iterate over each sub-array in the two-dimensional array. During each iteration, we merge all the arrays into one array using the array merge operator " ". Finally, we output the returned results to see the results.

The third method is to use the array_walk_recursive function. This function makes a callback for each element in a multidimensional array. We can use this function to operate on each element in the two-dimensional array. The implementation code is as follows:

$sums = array();

array_walk_recursive($array, function ($value, $key) use (&$sums) {
  if (isset($sums[$key])) {
    $sums[$key] += $value;
  }
  else {
    $sums[$key] = $value;
  }
});

print_r($sums);

In this code, we first create a new array named $sums. We use the array_walk_recursive function to make a callback for each element in the two-dimensional array, such as the value and key of the currently traversed element. In each callback, we check if the current key already exists in $sums and then add its value to the existing value or add it to $sums. Finally, we print $sums to see the results.

To summarize, we can use different methods such as loops, functions, and callback functions to sum the same elements in a two-dimensional array in PHP. It depends on your specific needs and preferences. No matter which method you use, you can easily handle various operations on two-dimensional arrays by judicious use of PHP built-in functions.

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