@ -110,29 +110,86 @@ $result = ArrayHelper::getColumn($array, function ($element) {
## Re-indexing Arrays < span id = "reindexing-arrays" > < / span >
In order to index an array according to a specified key, the `index` method can be used. The input array should be
multidimensional or an array of objects. The key can be a key name of the sub-array, a property name of object, or
an anonymous function which returns the key value given an array element .
multidimensional or an array of objects. The `$ key` either a key name of the sub-array, a property name of
object, or an anonymous function that must return the value that will be used as a key .
If a key value is null, the corresponding array element will be discarded and not put in the result. For example,
The `$groupBy` attribute is the array of keys, that will be used to group the input array by one or more keys.
If the `$key` attribute or its value for the particular element is null and `$groupBy` is not defined, the array
element will be discarded. Otherwise, if `$groupBy` is specified, array element will be added to the result array
without any key.
For example:
```php
$array = [
['id' => '123', 'data' => 'abc'],
['id' => '345', 'data' => 'def'],
['id' => '123', 'data' => 'abc', 'device' => 'laptop'],
['id' => '345', 'data' => 'def', 'device' => 'tablet'],
['id' => '345', 'data' => 'hgi', 'device' => 'smartphone'],
];
$result = ArrayHelper::index($array, 'id');
// the result is:
// [
// '123' => ['id' => '123', 'data' => 'abc'],
// '345' => ['id' => '345', 'data' => 'def'],
// ]
```
// using anonymous function
The result will be an associative array, where the key is the value of `id` attribute
```php
[
'123' => ['id' => '123', 'data' => 'abc', 'device' => 'laptop'],
'345' => ['id' => '345', 'data' => 'hgi', 'device' => 'smartphone']
// The second element of the original array is overridden by the last array element with the same key value
]
```
Anonymous function, passed as a `$key` , gives the same result.
```php
$result = ArrayHelper::index($array, function ($element) {
return $element['id'];
});
```
Passing `id` as the third argument will group the $array by the `id` value:
```php
$result = ArrayHelper::index($array, null, 'id');
```
The result will be a multidimensional array grouped by `id` on the first level and not indexed on the second level:
```php
[
'123' => [
['id' => '123', 'data' => 'abc', 'device' => 'laptop']
],
'345' => [ // all elements with this index are present in the result array
['id' => '345', 'data' => 'def', 'device' => 'tablet'],
['id' => '345', 'data' => 'hgi', 'device' => 'smartphone'],
]
]
```
The anonymous function can be used in the array of grouping keys as well:
```php
$result = ArrayHelper::index($array, 'data', [function ($element) {
return $element['id'];
}, 'device']);
```
The result will be a multidimensional array grouped by `id` on the first level, by the `device` on the second one
and indexed by the `data` on the third level:
```php
[
'123' => [
'laptop' => [
'abc' => ['id' => '123', 'data' => 'abc', 'device' => 'laptop']
]
],
'345' => [
'tablet' => [
'def' => ['id' => '345', 'data' => 'def', 'device' => 'tablet']
],
'smartphone' => [
'hgi' => ['id' => '345', 'data' => 'hgi', 'device' => 'smartphone']
]
]
]
```
## Building Maps < span id = "building-maps" > < / span >
SilverFire - Dmitry Naumenko
9 years ago