title: PHP Array Cheat Sheet
tags: php array cheat-sheet

```php
$arr_a = array(1,2,3);
$arr_b = [4,5,6];
$arr_c = ["hello"=>"world"];
$arr_d = array("hello"=>"world");
$a = array_pop($arr_a);
$b = array_shift($arr_b);
array_unshift($arr_a,5,6,7);
array_push($arr_b,9,8,7);
```

Note that with `array_filter` the array comes first;
with `array_map`, the function comes first. Note that
`array_map` can take more than one array as arguments.
```php
$arr_c = array_filter($arr_a,function($x) { return true; });
$arr_d = array_map(function($x) { return "hello $x"; }, $arr_a, $arr_b);
```

```php
if( count($arr_a) > 0 ) { ... }
if( array_key_exists("hello",$arr_a) ) { ... }
if( isset($arr_a["hello"]) ) { ... }
if( in_array("world",$arr_a) ) { ... }
```
```php
$xs = explode(",","hello,world");
$y = implode(":",$xs);
```

### Reindexing
If we filter and don't reindex, then `json_encode` will return
a `{"dict":"object"}` and not an `[a,r,r,a,y]`. To reindex:
```php
$arr_e = array_values($arr_d);
```
Also there is
```php
$keys = array_keys($arr_e);
```