Categorise objects in a associative array grouped by a object property - php

Question

Let me first explain my problem.
I have a simple value object Poi. Private properties and getters/setters are left out for sake of simplicity in this example.
class Poi implements JsonSerializable
{
public $latitude;
public $longitude;
public $category;
public function __construct($category, $lat, $long)
{
$this->category = $category;
$this->latitude = $lat;
$this->longitude = $long;
}
public function jsonSerialize()
{
return array(
'lat' => $this->latitude,
'lng' => $this->longitude,
);
}
}
Some dataproviders are responsible for returning a array of Poi's. i.e.
class PoiProvider1
{
public function getPois()
{
return array(
new Poi('airport', 10, 10),
new Poi('airport', 10, 15),
new Poi('restaurant', 30, 30),
)
}
}
class PoiProvider2
{
public function getPois()
{
return array(
new Poi('hotel', 20, 20),
new Poi('airport', 30, 30),
)
}
}
Now I want an array structured a follows, which I can json_encode()
array(
'airport' => array(
new Poi('airport', 10, 10),
new Poi('airport', 10, 15),
new Poi('airport', 30, 30),
),
'restaurant' => array(
new Poi('restaurant', 30, 30),
),
'hotel' => array(
new Poi('hotel', 20, 20),
)
);
Which after a json_encode will end up in the following structure:
{
"airport":[
{"lat":10,"lng":10},
{"lat":10,"lng":15},
{"lat":30,"lng":30}
],
"restaurant":[
{"lat":30,"lng":30}
],
"hotel":[
{"lat":20,"lng":20}
]
}
I can create such a structure using array_merge and some array copying, like this:
$provider1 = new PoiProvider1();
$provider2 = new PoiProvider2();
$pois = array_merge($provider1->getPois(), $provider2->getPois());
$poisNew = array();
foreach ($pois as $poi)
{
$poisNew[$poi->category][] = $poi;
}
Obviously this is memory consuming and slow when dealing with lots of poi's.
There must be some nicer and faster way (i.e. using Iterators), but I'm not sure how to approach this. Could anyone give me some pointers how to proceed?

Answer 1

For speeding things up eliminate post processing.
ELIMINATION OF POST PROCESSING:
You can use another global or class static container for pois which auto indexes and stores them during construction like this:
class Poi implements JsonSerializable {
public static $json; // this is our new hero.
public $latitude;
public $longitude;
public $category;
public function __construct($category, $lat, $long){
$this->category = $category;
$this->latitude = $lat;
$this->longitude = $long;
array_push(self::$json[$category], $this); // this does the trick...
}
public function jsonSerialize()
{
return array(
'lat' => $this->latitude,
'lng' => $this->longitude,
);
}
}
Poi::$json = array();
Now at each poi creation, the poi instances are stored into Poi::$json exactly in the form you need.
GENERATING POI'S:
If you do not need to process poi's, this will simplify your providers also:
class PoiProvider1 {
public function getPois(){ // no need to return if they are just for json.
new Poi('airport', 10, 10); // because each instance will be autoMagically
new Poi('airport', 10, 15); // added to Poi::$json
new Poi('restaurant', 30, 30);
}
}
But if you do something else on poi instances do not use the code above...
ENCODING:
Since $json is an associated array you can get the required output effect by using
json_encode((object)Poi::$json);
The drawback is poi's will stick in memory and survive gc because they are reachable via Poi::$json. So after you json_encode set
Poi::$json = null;
I hope this helps.