Can't concatenate 2 arrays in PHP

问题

I've recently learned how to join 2 arrays using the + operator in PHP.

But consider this code...

$array = array('Item 1');

$array += array('Item 2');

var_dump($array);

Output is

array(1) { [0]=> string(6) "Item 1" }

Why does this not work? Skipping the shorthand and using $array = $array + array('Item 2') does not work either. Does it have something to do with the keys?

回答1:

Both will have a key of 0, and that method of combining the arrays will collapse duplicates. Try using array_merge() instead.

$arr1 = array('foo'); // Same as array(0 => 'foo')
$arr2 = array('bar'); // Same as array(0 => 'bar')

// Will contain array('foo', 'bar');
$combined = array_merge($arr1, $arr2);

If the elements in your array used different keys, the + operator would be more appropriate.

$arr1 = array('one' => 'foo');
$arr2 = array('two' => 'bar');

// Will contain array('one' => 'foo', 'two' => 'bar');
$combined = $arr1 + $arr2;

Edit: Added a code snippet to clarify

回答2:

Use array_merge()
See the documentation here:
http://php.net/manual/en/function.array-merge.php

Merges the elements of one or more arrays together so that the values of one are appended to the end of the previous one. It returns the resulting array.

回答3:

+ is called the Union operator, which differs from a Concatenation operator (PHP doesn't have one for arrays). The description clearly says:

The + operator appends elements of remaining keys from the right handed array to the left handed, whereas duplicated keys are NOT overwritten.

With the example:

$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");
$c = $a + $b;

array(3) {
  ["a"]=>
  string(5) "apple"
  ["b"]=>
  string(6) "banana"
  ["c"]=>
  string(6) "cherry"
}

Since both your arrays have one entry with the key 0, the result is expected.

To concatenate, use array_merge.

回答4:

All previous answers are incorrect! merge actually merges the arrays, meaning, if the arrays have a common item one of the copies will be omitted. Same goes for union.

I didn't find a "work-around" for this issue, but to actually do it manually...

here it goes:

<?php
$part1 = array(1,2,3);
echo "array 1 = \n";
print_r($part1);
$part2 = array(4,5,6);
echo "array 2 = \n";
print_r($part2);
$ans = NULL;
for ($i = 0; $i < count($part1); $i++) {
    $ans[] = $part1[$i];
}
for ($i = 0; $i < count($part2); $i++) {
    $ans[] = $part2[$i];
}
echo "after arrays concatenation:\n";
print_r($ans);
?>

回答5:

Try array_merge.

$array1 = array('Item 1');

$array2 = array('Item 2');

$array3 = array_merge($array1, $array2);

I think its because you are not assigning a key to either, so they both have key of 0, and the + does not re-index, so its trying to over write it.

回答6:

$array = array('Item 1');

array_push($array,'Item 2');

$array[] = 'Item 2';

回答7:

It is indeed a key conflict. When concatenating arrays, duplicate keys are not overwritten.

Instead you must use array_merge()

$array = array_merge(array('Item 1'), array('Item 2'));

回答8:

This works for non-associative arrays:

while(($item = array_shift($array2)) !== null && array_push($array1, $item));

回答9:

Try saying

$array[] = array('Item 2');

Although it looks like you're trying to add an array into an array, thus $array[][] but that's not what your title suggests.

回答10:

you may use operator . $array3 = $array1.$array2;

来源：https://stackoverflow.com/questions/2650177/cant-concatenate-2-arrays-in-php

标签

php

arrays

concatenation