Syntax: select (selectorValue {(v, k) ==> result} [, selectorKey {(v, k) ==> result}])
This projection method requires the transform functions, selectorValue and selectorKey, to produce one key-value pair for each value in the source sequence. If selectorValue returns a value that is itself a collection, it is up to the consumer to traverse the subsequences manually. In such a situation, it might be better for your query to return a single coalesced sequence of values. To achieve this, use the {@link selectMany()} method instead of select. Although selectMany works similarly to select, it differs in that the transform function returns a collection that is then expanded by selectMany before it is returned.
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public select ( callable $selectorValue, callable | null $selectorKey = null ) : |
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| $selectorValue | callable | {(v, k) ==> value} A transform function to apply to each value. |
| $selectorKey | callable | null | {(v, k) ==> key} A transform function to apply to each key. Default: key. |
| return | A sequence whose elements are the result of invoking the transform functions on each element of source. | |
public function select($selectorValue, $selectorKey = null)
{
$selectorValue = Utils::createLambda($selectorValue, 'v,k');
$selectorKey = Utils::createLambda($selectorKey, 'v,k', Functions::$key);
return new self(function () use($selectorValue, $selectorKey) {
foreach ($this as $k => $v) {
(yield $selectorKey($v, $k) => $selectorValue($v, $k));
}
});
} /** {@inheritdoc} */
public function getIterator()
{
$orders = [];
for ($order = $this; $order != null; $order = $order->parent) {
$orders[] = $order;
}
$orders = array_reverse($orders);
$map = $this->source->select(function ($v, $k) {
return ['v' => $v, 'k' => $k];
})->toList();
$comparers = [];
for ($i = 0; $i < count($orders); ++$i) {
$order = $orders[$i];
$comparer = $order->comparer;
if ($order->desc) {
$comparer = function ($a, $b) use($comparer) {
return -$comparer($a, $b);
};
}
$comparers[] = $comparer;
for ($j = 0; $j < count($map); ++$j) {
$keySelector = $order->keySelector;
$map[$j][] = $keySelector($map[$j]['v'], $map[$j]['k']);
}
}
usort($map, function ($a, $b) use($comparers) {
for ($i = 0; $i < count($comparers); ++$i) {
$diff = $comparers[$i]($a[$i], $b[$i]);
if ($diff != 0) {
return $diff;
}
}
return 0;
});
return Enumerable::from($map)->select(function ($v) {
return $v['v'];
}, function ($v) {
return $v['k'];
})->getIterator();
}
