php index array and associative array

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I encountered a bug recently and recorded it. The printing results of

//定义一个数组
$arr = Array('a','b','c','d');

//转为json字符串
$str1 = json_encode($arr);

//去掉一项
unset($arr[1]);

//转json
$str2 = json_encode($arr);

var_dump($str1);
echo &#39;<br/>&#39;;
var_dump($str2);

string(17) "["a","b","c","d"]"

string(25) "{"0":"a","2":"c","3":"d"}"

show that one is an array and the other is an object.

Obviously the first is an index array and the second is an associative array. The index array is converted to json to an array, and the associative array is converted to json to an object.

Directly using unset() to delete array elements will convert the index array into an associative array

How to delete elements and keep the index:

unset($arr[1]);
array_values($arr);

array_splice($array, 1, 1);

Related recommendations:

PHP index array is processed into an associative array on demand?

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