What to do if the array is empty after php merge

As a widely used programming language, PHP has very powerful array operation functions. Among them, merging arrays is one of the very practical functions. However, in actual use, we sometimes find that the merged array is empty, so what is going on?

1. Basic methods of array merging

Let’s first review the basic methods of array merging in PHP. In PHP, there are three functions that can be used to merge arrays, namely array_merge(), array_merge_recursive() and operator.

1. array_merge() function

This function is used to merge the values ​​of two or more arrays into one array and return the merged array. It is used as follows:

$resultArray = array_merge($array1, $array2);

array_merge() can use any number of arrays, and for the same key name, only the value corresponding to the last key name is retained, and the values ​​corresponding to the previous key names will be ignored. .

2. array_merge_recursive() function

This function is similar to the array_merge() function, but it will recursively merge two or more arrays into one array and return the merged array. . It is used as follows:

$resultArray = array_merge_recursive($array1, $array2);

array_merge_recursive() can also use any number of arrays, and for the same key name, it will merge the values ​​into a single array.

3. Operator

In PHP, you can also use the operator to merge arrays, which will merge the values ​​of two arrays into one array and return the merged array. It is used as follows:

$resultArray = $array1 + $array2;

The operator can also be used on any number of arrays. For the same key name, only the value corresponding to the first array is retained, and the values ​​corresponding to the subsequent arrays are ignored.

2. The situation when the merged array is empty

When we use the above three methods to merge arrays, sometimes we will find that the merged result is an empty array. This situation is very disappointing. Confused. So why does this happen?

1. Key name conflict causes merge failure

When using the above three methods to merge arrays, if the same key name exists in the two arrays, the merge operation may fail. The combined result is an empty array.

For example, there are two arrays $array1 and $array2, their key names are the same, the arrays are as follows:

$array1 = array("a" => "A", "b" => "B");
$array2 = array("a" => "AA", "c" => "C");

If we use the array_merge() function to merge, as follows:

$resultArray = array_merge($array1, $array2);

The merge operation will fail due to key name conflict, and the result of $resultArray will be an empty array.

Similarly, if we use the array_merge_recursive() function to merge, as shown below:

$resultArray = array_merge_recursive($array1, $array2);

The merge operation will fail due to key name conflicts, and the result of $resultArray will also be an empty array.

If we use the operator to merge, as shown below:

$resultArray = $array1 + $array2;

The merge operation will fail also due to key name conflicts, and the result of $resultArray will still be an empty array.

2. The merge fails due to empty arrays

In addition to key name conflicts, if one or both arrays in the two arrays are empty, the merge operation will also fail. The result is an empty array.

For example, if an array is an empty array, as shown below:

$array1 = array();
$array2 = array("a" => "A");

If we use the array_merge() function to merge, as shown below:

$resultArray = array_merge($array1, $array2);

Then due to the array $array1 is an empty array, the merge operation will fail, and the result of $resultArray is an empty array.

Similarly, if we use the array_merge_recursive() function to merge, as shown below:

$resultArray = array_merge_recursive($array1, $array2);

The merge operation will fail because the array $array1 is an empty array, and the result of $resultArray will also be empty. array.

If we use the operator to merge, as follows:

$resultArray = $array1 + $array2;

Then since the array $array1 is an empty array, the result of $resultArray is $array2 itself, that is, $resultArray = $array2.

3. Prevent array merging from failing

In order to avoid empty arrays when merging arrays using the above three methods, we can use some methods to prevent this situation.

1. Use the isset() function to determine whether an array is empty

When using the above three methods to merge arrays, we can use the isset() function to determine whether an array is empty. This avoids merge failures.

For example, if we want to merge the arrays $array1 and $array2, we can determine whether the array is empty like this:

if (isset($array1) && isset($array2)) {
    $resultArray = array_merge($array1, $array2);
}

This way we can avoid the situation where $arrays1 or $array2 is empty.

Similarly, when we can use the array_merge_recursive() function or operator, we can also use the isset() function to determine whether the array is empty.

2. Use the array() function to initialize the array

When using the above three methods to merge arrays, we can also use the array() function to initialize the array when the array is empty. This avoids merge failures.

For example, if we have an empty array $emptyArray, we can initialize it like this:

$emptyArray = array();

In this way, when using the array_merge() function, array_merge_recursive() function or operator, if you want To merge the arrays $emptyArray and $array2, you can do this:

$resultArray = array_merge($emptyArray, $array2);

This way there will be no merge failure.

3. Summary

Arrays are one of the most powerful functions in PHP, and merging arrays is also a common operation. But in actual applications, we sometimes find that the merged array is empty. At this time, the reason may be caused by key name conflict, or it may be caused by the array being empty. In order to avoid this situation, we can use the isset() function to determine whether the array is empty, and use the array() function to initialize the array. In this way, we can successfully complete the array merging operation.

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