PHP code example of dusank / knapsack

    
        
<?php
require_once('vendor/autoload.php');

/* Start to develop here. Best regards https://php-download.com/ */

    

dusank / knapsack example snippets

use DusanKasan\Knapsack\Collection;

$collection1 = new Collection([1, 2, 3]);
$collection2 = Collection::from([1, 2, 3]); //preferred since you can call methods on its result directly.

$collection1 = Collection::from([1, 2, 3]);
$collection2 = Collection::from(new ArrayIterator([1, 2, 3]);

//Used because Generator can not be rewound
$collection2 = Collection::from(function() { //must have 0 arguments
    foreach ([1, 2, 3] as $value) {
        yield $value;
    }
});

$result = Collection::from([1, 2])
    ->map(function($v) {return $v*2;})
    ->reduce(function($tmp, $v) {return $tmp+$v;}, 0);
    
echo $result; //6

$result = reduce(
    map(
        [1, 2], 
        function($v) {return $v*2;}
    ),
    function($tmp, $v) {return $tmp+$v;},
    0
);

echo $result; //6

$result = Collection::iterate([1,1], function($v) {
        return [$v[1], $v[0] + $v[1]]; //[1, 2], [2, 3] ...
    })
    ->map('\DusanKasan\Knapsack\first') //one of the collection functions
    ->take(5);
    
foreach ($result as $item) {
    echo $item . PHP_EOL;
}

//1
//1
//2
//3
//5

$result = Collection::from([[[1]]])
    ->first(true)
    ->first();
    
var_dump($result); //[1]

function multiplyBy2($v)
{
    return $v * 2;
}

function multiplyBy3($v)
{
    return $v * 3;
}

function add($a, $b)
{
    return $a + $b;
}

$collection = Collection::from([1, 2]);

$result = $collection
    ->map('multiplyBy2')
    ->reduce(0, 'add');
    
echo $result; //6

//On the same collection
$differentResult = $collection
    ->map('multiplyBy3')
    ->reduce(0, 'add');
    
echo $differentResult; //9

$result = Collection::from([1, 2])->concat([3,4]);
    
//arrays have unique keys
$result->toArray(); //[3,4]
$result->values()->toArray(); //[1, 2, 3, 4]

//When iterating, you can have multiple keys.
foreach ($result as $key => $item) {
    echo $key . ':' . $item . PHP_EOL;
}

//0:1
//1:2
//0:3
//1:4

class AwesomeIterator extends ArrayIterator {
    use CollectionTrait;
}

$iterator = new AwesomeIterator([1, 2, 3]);
$iterator->size(); //3

+------------------------------------------------------------------------------------+-----------------------+---------------------------+----------------------+
| operation details                                                                  | native execution time | collection execution time | difference (percent) |
+------------------------------------------------------------------------------------+-----------------------+---------------------------+----------------------+
| array_map vs Collection::map on 10000 integers (addition)                          | 0.0034945011138916s   | 0.0034625053405762s       | 99%                  |
| array_map vs Collection::map on 10000 strings (concatenation)                      | 0.004361891746521s    | 0.0049739360809326s       | 114%                 |
| array_map vs Collection::map on 10000 objects (object to field value)              | 0.02332329750061s     | 0.027161455154419s        | 116%                 |
| array_map vs Collection::map on 10000 md5 invocations                              | 0.0086771726608276s   | 0.0080755949020386s       | 93%                  |
| array_map vs Collection::map on 10000 integers n, counting sum(0, n) the naive way | 1.5985415458679s      | 1.580038356781s           | 98%                  |
+------------------------------------------------------------------------------------+-----------------------+---------------------------+----------------------+

+------------------------------------------------------------------------------------+-----------------------+---------------------------+----------------------+
| operation details                                                                  | native execution time | collection execution time | difference (percent) |
+------------------------------------------------------------------------------------+-----------------------+---------------------------+----------------------+
| array_map vs Collection::map on 10000 integers (addition)                          | 0.00082111358642578s  | 0.001681661605835s        | 204%                 |
| array_map vs Collection::map on 10000 strings (concatenation)                      | 0.00081214904785156s  | 0.0015116214752197s       | 186%                 |
| array_map vs Collection::map on 10000 objects (object to field value)              | 0.0015491008758545s   | 0.0036969423294067s       | 238%                 |
| array_map vs Collection::map on 10000 md5 invocations                              | 0.0032038688659668s   | 0.0039427280426025s       | 123%                 |
| array_map vs Collection::map on 10000 integers n, counting sum(0, n) the naive way | 0.93844709396362s     | 0.93354930877686s         | 99%                  |
+------------------------------------------------------------------------------------+-----------------------+---------------------------+----------------------+

$collection = new Collection([1, 2, 3]);

$collection = new Collection(new ArrayIterator([1, 2, 3]));

$generatorFactory = function () {
    foreach ([1, 2] as $value) {
        yield $value;
    }
};

$collection = new Collection($generatorFactory);

$collection = Collection::from([1, 2, 3]);

$collection = Collection::from(new ArrayIterator([1, 2, 3]));

$generatorFactory = function () {
    foreach ([1, 2] as $value) {
        yield $value;
    }
};

$collection = Collection::from($generatorFactory);

$collection = Collection::iterate(1, function ($value) {return $value + 1;}); // 1, 2, 3, 4 ...

Collection::repeat(1); //infinite collection of ones

Collection::repeat(1, 4)->toArray(); //[1, 1, 1, 1]

Collection::range(0, 6, 2)->toArray(); //[0, 2, 4, 6]

Collection::from([1, 3, 3, 2])
    ->append(1)
    ->toArray(); //[1, 3, 3, 2, 1]

Collection::from([1, 3, 3, 2])
    ->append(1, 'key')
    ->toArray(); //[1, 3, 3, 2, 'key' => 1]

toArray(append([1, 3, 3, 2], 1, 'key')); //[1, 3, 3, 2, 'key' => 1]

Collection::from([1, 2, 3, 2])->average(); //2
Collection::from([1, 2, 3, 2, 2])->average(); //2.2
Collection::from([])->average(); //0

average([1, 2, 3]); //2

Collection::from(['a', 'b'])
    ->combine([1, 2])
    ->toArray(); //['a' => 1, 'b' => 2]

toArray(combine(['a', 'b'], [1, 2])); //['a' => 1, 'b' => 2]

Collection::from([1, 3, 3, 2])
    ->concat([4, 5]) //If we would convert to array here, we would loose 2 items because of same keys [4, 5, 3, 2]
    ->values() 
    ->toArray(); //[1, 3, 3, 2, 4, 5]

toArray(values(concat([1, 3, 3, 2], [4, 5]))); //[1, 3, 3, 2, 4, 5]  

Collection::from([1, 3, 3, 2])->contains(2); //true

contains([1, 3, 3, 2], 2); //true

Collection::from([1, 2, 3, 4, 5])
    ->countBy(function ($value) {
        return $value % 2 == 0 ? 'even' : 'odd';
    })
    ->toArray(); //['odd' => 3, 'even' => 2]  

toArray(countBy([1, 2, 3, 4, 5], function ($value) {return $value % 2 == 0 ? 'even' : 'odd';}));      

Collection::from([1, 3, 3, 2])
    ->cycle()
    ->take(8) //we take just 8 items, since this collection is infinite
    ->values()
    ->toArray(); //[1, 3, 3, 2, 1, 3, 3, 2]

toArray(values(take(cycle([1, 3, 3, 2]), 8))); //[1, 3, 3, 2, 1, 3, 3, 2]

Collection::from([1, 3, 3, 2])
    ->diff([1, 3])
    ->toArray(); //[3 => 2]

toArray(diff([1, 3, 3, 2], [1, 3])); //[3 => 2]

Collection::from([1, 3, 3, 2])
    ->distinct()
    ->toArray(); //[1, 3, 3 => 2] - each item has key of the first occurrence

toArray(distinct([1, 3, 3, 2])); //[1, 3, 3 => 2] - each item has key of the first occurrence

Collection::from([1, 2, 3, 4, 5])
    ->drop(4)
    ->toArray(); //[4 => 5]

toArray(drop([1, 2, 3, 4, 5], 4)); //[4 => 5]    

Collection::from([1, 2, 3])
    ->dropLast()
    ->toArray(); //[1, 2]

Collection::from([1, 2, 3])
$collection
    ->dropLast(2)
    ->toArray(); //[1]

toArray(dropLast([1, 2, 3], 2)); //[1]    

Collection::from([1, 3, 3, 2])
    ->dropWhile(function ($v) {
        return $v < 3;
    })
    ->toArray(); //[1 => 3, 2 => 3, 3 => 2])

Collection::from([1, 3, 3, 2])
    ->dropWhile(function ($v, $k) {
        return $k < 2 && $v < 3;
    })
    ->toArray(); //[1 => 3, 2 => 3, 3 => 2])

Collection::from([1, 3, 3, 2])
    ->dropWhile(function ($v, $k) {
        return $k < 2 && $v < 3;
    })
    ->toArray(); //[1 => 3, 2 => 3, 3 => 2])

toArray(values(dropWhile([1, 3, 3, 2], function ($v) {return $v < 3;}))); // [3, 3, 2]

Collection::from([1, 3, 3, 2])->dump(); //[1, 3, 3, 2]

$collection = Collection::from(
    [
        [
            [1, [2], 3],
            ['a' => 'b'],
            new ArrayIterator([1, 2, 3])
        ],
        [1, 2, 3],
        new ArrayIterator(['a', 'b', 'c']),
        true,
        new \DusanKasan\Knapsack\Tests\Helpers\Car('sedan', 5),
        \DusanKasan\Knapsack\concat([1], [1])
    ]
);

$collection->dump(2, 3);
//[
//    [
//        [1, '^^^', '>>>'],
//        ['a' => 'b'],
//        '>>>'
//    ],
//    [1, 2, '>>>'],
//    '>>>'
//]

$collection->dump();
//[
//    [
//        [1, [2], 3],
//        ['a' => 'b'],
//        [1, 2, 3]
//    ],
//    [1, 2, 3],
//    ['a', 'b', 'c'],
//    true,
//    [
//        'DusanKasan\Knapsack\Tests\Helpers\Car' => [
//            'numberOfSeats' => 5,
//        ],
//    ],
//    [1, '0//1' => 1]
//]

dump([1, 3, 3, 2], 2); // [1, 3, '>>>']

Collection::from([1, 2, 3, 4, 5])
    ->each(function ($i) {
        echo $i . PHP_EOL;
    })
    ->toArray(); //[1, 2, 3, 4, 5]

//1
//2
//3
//4
//5

each([1, 2, 3, 4, 5], function ($v) {echo $v . PHP_EOL;});

//1
//2
//3
//4
//5

Collection::from([1, 3, 3, 2])
    ->every(function ($v) {
        return $v < 3;
    }); //false

Collection::from([1, 3, 3, 2])
    ->every(function ($v, $k) {
       return $v < 4 && $k < 2;
    }); //false

every([1, 3, 3, 2], function ($v) {return $v < 5;}); //true

Collection::from(['a' => 1, 'b' => 2])
    ->except(['a'])
    ->toArray(); //['b' => 2]

toArray(except(['a' => 1, 'b' => 2], ['a'])); //['b' => 2]

$collection = Collection::from([['a' => ['b' => 1]], ['a' => ['b' => 2]], ['c' => ['b' => 3]]])
$collection->extract('a.b')->toArray(); //[1, 2]
$collection->extract('*.b')->toArray(); //[1, 2, 3]

toArray(extract([['a' => ['b' => 1]], ['a' => ['b' => 2]]], 'a.b')); //[1, 2]

Collection::from([1, 3, 3, 2])
    ->filter(function ($value) {
        return $value > 2;
    })
    ->values()
    ->toArray(); //[3, 3]

Collection::from([1, 3, 3, 2])
    ->filter(function ($value, $key) {
        return $value > 2 && $key > 1;
    })
    ->toArray(); //[2 => 3]

toArray(values(filter([1, 3, 3, 2], function ($value) {return $value > 2;}))); //[3, 3]

Collection::from([0, 0.0, false, null, "", []])
    ->filter()
    ->isEmpty(); //true

isEmpty(values(filter([0, 0.0, false, null, "", []]))); //true

Collection::from([1, 3, 3, 2])
    ->find(function ($value) {
       return $value < 3;
    }); //1

Collection::from([1, 3, 3, 2])
    ->find(function ($value) {
       return $value > 3;
    }, 10); //10

Collection::from([1, 3, 3, 2])
    ->find(function ($value, $key) {
      return $value < 3 && $key > 1;
    }); //2

//if the output can be converted to Collection (it's array or Traversable), it will be.
Collection::from([1, [4, 5], 3, 2])
    ->find(function ($value) {
      return is_array($value);
    }, [], true)
    ->size(); //2 

find([1, 3, 3, 2], function ($value) {return $value > 2;}); //3

Collection::from([1, 2, 3])->first(); //1

Collection::from([[1], 2, 3])->first(); //[1]

Collection::from([])->first(); //throws ItemNotFound

first([1, 2, 3]); //1

Collection::from([1,[2, [3]]])
    ->flatten()
    ->values() //1, 2 and 3 have all key 0
    ->toArray(); //[1, 2, 3]

Collection::from([1,[2, [3]]])
    ->flatten(1)
    ->values() //1, 2 and 3 have all key 0
    ->toArray(); //[1, 2, [3]]

toArray(values(flatten([1, [2, [3]]]))); //[1, 2, 3]

Collection::from(['a' => 0, 'b' => 1])
    ->flip()
    ->toArray(); //['a', 'b']

toArray(flip(['a' => 0, 'b' => 1])); //['a', 'b']

Collection::from([1, 3, 3, 2])
    ->frequencies()
    ->toArray(); //[1 => 1, 3 => 2, 2 => 1]

toArray(frequencies([1, 3, 3, 2])); //[1 => 1, 3 => 2, 2 => 1]

Collection::from([1, 3, 3, 2])->get(2); //3

Collection::from([1, [1, 2]])->get(1, true)->toArray(); //[1, 2]

Collection::from([1, 3, 3, 2])->get(5); //throws ItemNotFound

get([1, 3, 3, 2], 2); //3

Collection::from([1, 3, 3, 2])->getOrDefault(2); //3

Collection::from([1, 3, 3, 2])->getOrDefault(5); //null

Collection::from([1, 3, 3, 2])->getOrDefault(5, 'asd'); //'asd'

Collection::from([1, 3, 3, 2])->getOrDefault(5, [1, 2], true)->toArray(); //[1, 2]

getOrDefault([1, 3, 3, 2], 5, 'asd'); //'asd'

Collection::from([1, 2, 3, 4, 5])
    ->groupBy(function ($value) {
        return $value % 2;
    })
    ->toArray(); //[1 => [1, 3, 5], 0 => [2, 4]]

toArray(groupBy([1, 2, 3, 4, 5], function ($value) {return $value % 2;})); //[1 => [1, 3, 5], 0 => [2, 4]]

Collection::from([
        ['letter' => 'A', 'type' => 'caps'],
        ['letter' => 'a', 'type' => 'small'],
        ['letter' => 'B', 'type' => 'caps'],
    ])
    ->groupByKey('type')
    ->map('DusanKasan\Knapsack\toArray')
    ->toArray();
    // [ 'caps' => [['letter' => 'A', 'type' => 'caps'], ...], 'small' => [['letter' => 'a', 'type' => 'small']]]

$data = [
    ['letter' => 'A', 'type' => 'caps'],
    ['letter' => 'a', 'type' => 'small'],
    ['letter' => 'B', 'type' => 'caps'],
];
toArray(map(groupByKey($data, 'type'), 'toArray')); //[ 'caps' => [['letter' => 'A', 'type' => 'caps'], ...], 'small' => [['letter' => 'a', 'type' => 'small']]]

Collection::from(['a' => 1])->has('a'); //true

has(['a' => 1], 'a'); //true

Collection::from([1, 3, 3, 2])
    ->indexBy(function ($v) {
        return $v;
    })
    ->toArray(); //[1 => 1, 3 => 3, 2 => 2]

toArray(indexBy([1, 3, 3, 2], '\DusanKasan\Knapsack\identity')); //[1 => 1, 3 => 3, 2 => 2]

Collection::from([1, 3, 3, 2])
    ->interleave(['a', 'b', 'c', 'd', 'e'])
    ->values()
    ->toArray(); //[1, 'a', 3, 'b', 3, 'c', 2, 'd', 'e']

php
Collection::from([1, 2, 3])
    ->intersect([1, 3])
    ->toArray(); //[1, 2 => 3]

php
toArray(intersect([1, 2, 3],[1, 3])); //[1, 2 => 3] 

php
Collection::from([1, 3, 3, 2])->isEmpty(); //false

php
isEmpty([1]); //false

php
Collection::from([1, 3, 3, 2])->isNotEmpty(); //true

php
isNotEmpty([1]); //true

php
Collection::from([1, 2, 3])->last(); //3

php
Collection::from([1, 2, [3]])->last(true)->toArray(); //[1]

php
last([1, 2, 3]); //3

php
Collection::from([1, 3, 3, 2])
    ->map(function ($value) {
        return $value + 1;
    })
    ->toArray(); //[2, 4, 4, 3]

php
toArray(map([1, 3, 3, 2], '\DusanKasan\Knapsack\increment')); //[2, 4, 4, 3]

php
Collection::from([1, 3, 3, 2])
    ->mapcat(function ($value) {
        return [[$value]];
    })
    ->values()
    ->toArray(); //[[1], [3], [3], [2]]

php
Collection::from([1, 3, 3, 2])
    ->mapcat(function ($key, $value) {
        return [[$key]];
    })
    ->values()
    ->toArray(); //[[0], [1], [2], [3]]

php
toArray(values(mapcat([1, 3, 3, 2], function ($value) {return [[$value]];}))); //[[1], [3], [3], [2]]

php
Collection::from([1, 2, 3, 2])->max(); //3
Collection::from([])->max(); //null

php
max([1, 2, 3, 2]); //3

php
Collection::from([1, 2, 3, 2])->min(); //1
Collection::from([])->min(); //null

php
min([1, 2, 3, 2]); //1

php
Collection::from([1, 3, 3, 2])
    ->partition(3, 2, [0, 1])
    ->toArray(); //[[1, 3, 3], [2 => 3, 3 => 2, 0 => 0]]

php
Collection::from([1, 3, 3, 2])
    ->partition(3, 2)
    ->toArray(); //[[1, 3, 3], [2 => 3, 3 => 2]]

php
Collection::from([1, 3, 3, 2])
    ->partition(3)
    ->toArray(); //[[1, 3, 3], [3 => 2]]

php
toArray(partition([1, 3, 3, 2], 3)); //[[1, 3, 3], [3 => 2]]

php
Collection::from([1, 3, 3, 2])
    ->partitionBy(function ($v) {
        return $v % 3 == 0;
    })
    ->toArray(); //[[1], [1 => 3, 2 => 3], [3 => 2]]

php
toArray(partitionBy([1, 3, 3, 2], function ($value) {return $value % 3 == 0;})); //[[1], [1 => 3, 2 => 3], [3 => 2]]

php
Collection::from([1, 3, 3, 2])
    ->prepend(1)
    ->values() //both 1 have 0 key
    ->toArray(); //[1, 1, 3, 3, 2]

php
Collection::from([1, 3, 3, 2])
    ->printDump()
    ->toArray(); //[1, 3, 3, 2]

php
toArray(printDump([1, 3, 3, 2])); //[1, 3, 3, 2]

php
$helper->setValue(1); 

$realizedCollection = Collection::from([1, 3, 3, 2])
    ->map(function ($item) use ($helper) {return $helper->getValue() + $item;})
    ->realize();
    
$helper->setValue(10);
$realizedCollection->toArray(); // [2, 4, 4, 3]

php
toArray(realize([1, 3, 3, 2])); //[1, 3, 3, 2]

php
Collection::from([1, 3, 3, 2])
    ->reduce(
        function ($tmp, $i) {
            return $tmp + $i;
        }, 
        0
    ); //9
    
Collection::from([1, 3, 3, 2])
    ->reduce(
        function ($tmp, $i) {
            $tmp[] = $i + 1;
            return $tmp;
        }, 
        [],
        true
    )
    ->first(); //2

php
reduce([1, 3, 3, 2], function ($tmp, $value) {return $tmp + $value;}, 0); //9

php
Collection::from([1, 3, 3, 2])
    ->reduceRight(
        function ($tmp, $i) {
            return $tmp + $i;
        }, 
        0
    ); //9
    
Collection::from([1, 3, 3, 2])
    ->reduce(
        function ($tmp, $i) {
            $tmp[] = $i + 1;
            return $tmp;
        }, 
        [],
        true
    )
    ->first(); //3

php
reduceRight([1, 3, 3, 2], function ($tmp, $value) {return $tmp + $value;}, 0); //9

php
Collection::from([1, 3, 3, 2])
    ->reductions(function ($tmp, $i) {
        return $tmp + $i;
    }, 0)
    ->toArray(); //[1, 4, 7, 9]

php
toArray(reductions([1, 3, 3, 2], function ($tmp, $value) {return $tmp + $value;}, 0)); //[1, 4, 7, 9]

php
Collection::from([1, 3, 3, 2])
    ->reject(function ($value) {
        return $value > 2;
    })
    ->toArray(); //[1, 3 => 2]

php
Collection::from([1, 3, 3, 2])
    ->reject(function ($value, $key) {
        return $value > 2 && $key > 1;
    })
    ->toArray(); //[1, 1 => 3, 3 => 2]

php
toArray(reject([1, 3, 3, 2], function ($value) {return $value > 2;})); //[1, 1 => 3, 3 => 2]

php
toArray(replace([1, 3, 3, 2], [3 => 'a'])); //[1, 'a', 'a', 2]

php
toArray(replace([1, 3, 3, 2], [3 => 'a'])); //[1, 3, 3, 'a']

php
Collection::from([1, 2, 3])
    ->reverse()
    ->toArray(); //[2 => 3, 1 => 2, 0 => 1]

php
Collection::from([1, 3, 3, 2])->second(); //3

php
second([1, 3]); //3

php
Collection::from([1, 3, 3, 2])
    ->shuffle()
    ->toArray(); //something like [2 => 3, 0 => 1, 3 => 2, 1 => 3]

php
Collection::from([1, 3, 3, 2])->size(); //4

php
size([1, 3, 3, 2]); //4

php
Collection::from([1, 3, 3, 2])->sizeIsBetween(3, 5); //true

php
sizeIsBetween([1, 3, 3, 2], 3, 5); //true

php
Collection::from([1, 3, 3, 2])->sizeIs(4); //true

php
sizeIs([1, 3, 3, 2], 4); //true

php
Collection::from([1, 3, 3, 2])->sizeIsGreaterThan(3); //true

php
sizeIsGreaterThan([1, 3, 3, 2], 3); //true

php
Collection::from([1, 3, 3, 2])->sizeIsLessThan(5); //true

php
sizeIsLessThan([1, 3, 3, 2], 5); //true

php
Collection::from([1, 2, 3, 4, 5])
    ->slice(2, 4)
    ->toArray(); //[2 => 3, 3 => 4]

php
Collection::from([1, 2, 3, 4, 5])
    ->slice(4)
    ->toArray(); //[4 => 5]

php
toArray(slice([1, 2, 3, 4, 5], 4)); //[4 => 5]

php
Collection::from([1, 3, 3, 2])
    ->some(function ($value) {
       return $value < 3;
    }); //true

php
Collection::from([1, 3, 3, 2])
    ->some(function ($value, $key) {
       return $value < 4 && $key < 2;
    }); //true

php
some([1, 3, 3 ,2], function ($value) {return $value < 3;}); //true

php
Collection::from([3, 1, 2])
    ->sort(function ($a, $b) {
        return $a > $b;
    })
    ->toArray(); //[1 => 1, 2 => 2, 0 => 3]

php
Collection::from([3, 1, 2])
    ->sort(function ($v1, $v2, $k1, $k2) {
        return $v1 < $v2;
    })
    ->toArray(); //[2 => 2, 1 => 1, 0 => 3]

php
toArray(sort([3, 1, 2], function ($a, $b) {return $a > $b;})); //[1 => 1, 2 => 2, 0 => 3]

php
Collection::from([1, 3, 3, 2])
    ->splitAt(2)
    ->toArray(); //[[1, 3], [2 => 3, 3 => 2]]

php
toArray(splitAt([1, 3, 3, 2], 2)); //[[1, 3], [2 => 3, 3 => 2]]

php
Collection::from([1, 3, 3, 2])
    ->splitWith(function ($value) {
        return $value < 3;
    })
    ->toArray(); //[[1], [1 => 3, 2 => 3, 3 => 2]]

php
Collection::from([1, 3, 3, 2])
    ->splitWith(function ($value, $key) {
        return $key < 2 && $value < 3;
    })
    ->toArray(); //[[1], [1 => 3, 2 => 3, 3 => 2]]

php
toArray(splitWith([1, 3, 3, 2], function ($value) {return $value < 3;})); //[[1], [1 => 3, 2 => 3, 3 => 2]]

php
sum([1, 2, 3]); //6

php
toArray(take([1, 2, 3, 4, 5], 2)); //[1, 2]

php
Collection::from([1, 3, 3, 2])
    ->takeNth(2)
    ->toArray(); //[1, 2 => 3]

php
toArray(takeNth([1, 3, 3, 2], 2)); //[1, 2 => 3]

php
Collection::from([1, 3, 3, 2])
    ->takeWhile(function ($value) {
        return $value < 3;
    })
    ->toArray(); //[1]

php
Collection::from([1, 3, 3, 2])
    ->takeWhile(function ($value, $key) {
        return $key < 2 && $value < 3;
    })
    ->toArray(); //[1]

php
toArray(takeWhile([1, 3, 3, 2], function ($value) {return $value < 3;})); //[1]

php
$transformer = function (Collection $collection) {
    return $collection
        ->filter(function ($item) {
            return $item > 1;
        })
        ->map('\DusanKasan\Knapsack\increment');
};

Collection::from([1, 3, 3, 2])
    ->transform($transformer)
    ->toArray(); //[4, 4, 3]

php
Collection::from([1, 3, 3, 2])->toArray(); //[1, 3, 3, 2]

php
toArray([1, 3, 3, 2]); //[1, 3, 3, 2]

php
Collection::from([1, 'a', 3, null])->toString(); //'1a3'
Collection::from([])->toString(); //''

php
toString([1, 'a', 3, null]); //'1a3'

php
$value === identity($value); //true