talesoft/tale-iterator

A basic, PSR-7 compatible stream utility library

0.1.1 2018-08-24 12:42 UTC

This package is auto-updated.

Last update: 2020-11-10 00:02:01 UTC


README

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Tale Iterator

What is Tale Iterator?

Tale Iterator extends the SPL iterators by some more, useful iterators for common use-cases.

Installation

composer require talesoft/tale-iterator

Usage

MapIterator

Maps values by a map()-method. You mostly want to extend it and override the map()-method.

Stack with FlipIterator to map keys (see "How do I XYZ" at the bottom of this README)

use Tale\Iterator\MapIterator;

$values = new \ArrayIterator(range(0, 5));
$mapper = new class($values) extends MapIterator
{
    public function map()
    {
        return sprintf('Value %d', parent::map());
    }
};

var_dump(iterator_to_array($mapper));
/*
array(6) {
  [0] => string(7) "Value 0"
  [1] => string(7) "Value 1"
  [2] => string(7) "Value 2"
  [3] => string(7) "Value 3"
  [4] => string(7) "Value 4"
  [5] => string(7) "Value 5"
}
*/

CallbackMapIterator

Maps values by specifying a simple callback.

Stack with FlipIterator to map keys (see "How do I XYZ" at the bottom of this README)

use Tale\Iterator\CallbackMapIterator;

$values = new \ArrayIterator(range(0, 5));
$mapper = new CallbackMapIterator($values, function (int $number) {
    return sprintf('Value %d', $number);
});

var_dump(iterator_to_array($mapper));
/*
array(6) {
  [0] => string(7) "Value 0"
  [1] => string(7) "Value 1"
  [2] => string(7) "Value 2"
  [3] => string(7) "Value 3"
  [4] => string(7) "Value 4"
  [5] => string(7) "Value 5"
}
*/

FilterIterator

Filters values by an accept()-method. You mostly want to extend it and override the accept()-method. It will preserve keys!. If you want to reset the keys, chain a ValueIterator as shown below.

Stack with FlipIterator to filter keys (see "How do I XYZ" at the bottom of this README)

use Tale\Iterator\FilterIterator;

$values = new \ArrayIterator(range(0, 5));
$filterer = new class($values) extends FilterIterator
{
    public function accept(): bool
    {
        return parent::current() !== 4;
    }
};

var_dump(iterator_to_array($filterer));
/*
array(5) {
  [0] => string(7) "Value 0"
  [1] => string(7) "Value 1"
  [2] => string(7) "Value 2"
  [3] => string(7) "Value 3"
  [5] => string(7) "Value 5"
}
*/

CallbackFilterIterator

Filters values by specifying a simple callback.

Stack with FlipIterator to filter keys (see "How do I XYZ" at the bottom of this README)

use Tale\Iterator\CallbackFilterIterator;

$values = new \ArrayIterator(range(0, 5));
$filterer = new CallbackFilterIterator($values, function (int $number) {
    return $number !== 3;
});

var_dump(iterator_to_array($filterer));
/*
array(5) {
  [0] => string(7) "Value 0"
  [1] => string(7) "Value 1"
  [2] => string(7) "Value 2"
  [4] => string(7) "Value 4"
  [5] => string(7) "Value 5"
}
*/

Note:

PHP already has a FilterIterator and a CallbackFilterIterator, but it only accepts instances of \Iterator, which doesn't include \IteratorAggregate instances. This one accepts instances of \Traversable, which includes all iterables except for objects and native arrays (which are covered, too, keep reading). It uses the same API as the PHP implementation, though!

IterableIterator

This is a small utility iterator that turns any iterable into a valid iterator. It's equivalent to an \IteratorIterator, that normalizes the passed iterable to

$iterable instanceof \Traversable ? $iterable : new \ArrayIterator($iterable).

With this iterator, you can pass any kind of iterable, arrays, objects, generators etc. to an iterator that only accepts \Iterator instances easily.

This is useful for PHPs SPL iterators or other iterator implementations that don't leverage iterable or \Traversable and rely on \Iterator only and/or do this for a very good reason

use Tale\Iterator\IterableIterator;

$values = new IterableIterator(['a', 'b', 'c', 'd', 'e']);
$filterer = new \RegexIterator($values, '/[a-c]/');

var_dump(iterator_to_array($filterer));
/*
array(3) {
  [0] => string(1) "a"
  [1] => string(1) "b"
  [2] => string(1) "c"
}
*/

ValueIterator

This is basically array_values() for iterators. This is useful to e.g. reset the keys for FilterIterator outputs.

use Tale\Iterator\CallbackFilterIterator;
use Tale\Iterator\ValueIterator;

$values = new \ArrayIterator(range(0, 5));
$filterer = new CallbackFilterIterator($values, function (int $number) {
    return $number !== 3;
});
$resetter = new ValueIterator($filterer);

var_dump(iterator_to_array($resetter));
/*
array(5) {
  [0] => string(7) "Value 0"
  [1] => string(7) "Value 1"
  [2] => string(7) "Value 2"
  [3] => string(7) "Value 4"
  [4] => string(7) "Value 5"
}

Compare the output to the CallbackFilterIterator example above
and notice the keys!
*/

KeyIterator

This is basically array_keys() for iterators. This is useful if you want to get a clean list of the inner iterators keys.

use Tale\Iterator\KeyIterator;

$values = new \ArrayIterator(['a' => 1, 'b' => 2, 'c' => 3]);
$keys = new KeyIterator($values);

var_dump(iterator_to_array($keys));
/*
array(3) {
  [0] => string(1) "a"
  [1] => string(1) "b"
  [2] => string(1) "c"
}

Compare the output to the CallbackFilterIterator example above
and notice the keys!
*/

FlipIterator

This iterator will flip keys and values. This is often useful if you want outer iterators act on keys rather than on values.

Through the way iterators work, as long as you don't flatten the iterator to an array, duplicate values won't result on dropped keys! Notice the second example to understand what I mean.

use Tale\Iterator\FlipIterator;

$values = new \ArrayIterator(range('a', 'e'));
$flipper = new FlipIterator($values);

var_dump(iterator_to_array($flipper));
/*
array(5) {
  'a' => int(0)
  'b' => int(1)
  'c' => int(2)
  'd' => int(3)
  'e' => int(4)
}
*/

With array_flip, duplicate values will lead to dropped keys, as array keys have to be unique. With iterators, this isn't the case as long as you don't actually flatten it!

use Tale\Iterator\FlipIterator;

$values = new \ArrayIterator(['a' => 1, 'b' => 2, 'c' => 2, 'd' => 2]);
$flipper = new FlipIterator($values);

//Do something with $flipper, like, iterator stuff

$reverseFlipper = new FlipIterator($flipper);

var_dump(iterator_to_array($reverseFlipper));
/*
array(4) {
  'a' => int(1)
  'b' => int(2)
  'c' => int(2)
  'd' => int(2)
}
*/

FormatIterator

This is basically sprintf($format, $current) on each value in the iterator.

Stack with FlipIterator to format keys (see "How do I XYZ" at the bottom of this README)

use Tale\Iterator\FormatIterator;

$values = new \ArrayIterator(range(0, 5));
$formatter = new FormatIterator($values, 'Value %d');

var_dump(iterator_to_array($formatter));
/*
array(6) {
  [0] => string(7) "Value 0"
  [1] => string(7) "Value 1"
  [2] => string(7) "Value 2"
  [3] => string(7) "Value 3"
  [4] => string(7) "Value 4"
  [5] => string(7) "Value 5"
}
*/

PrefixIterator

This is $prefix.$current for each value in the iterator.

Stack with FlipIterator to prefix keys (see "How do I XYZ" at the bottom of this README)

use Tale\Iterator\PrefixIterator;

$values = new \ArrayIterator(range(0, 5));
$prefixer = new PrefixIterator($values, 'Value ');

var_dump(iterator_to_array($prefixer));
/*
array(6) {
  [0] => string(7) "Value 0"
  [1] => string(7) "Value 1"
  [2] => string(7) "Value 2"
  [3] => string(7) "Value 3"
  [4] => string(7) "Value 4"
  [5] => string(7) "Value 5"
}
*/

SuffixIterator

This is $current.$suffix for each value in the iterator.

Stack with FlipIterator to suffix keys (see "How do I XYZ" at the bottom of this README)

use Tale\Iterator\SuffixIterator;

$values = new \ArrayIterator(range(0, 5));
$suffixer = new SuffixIterator($values, ' Value');

var_dump(iterator_to_array($suffixer));
/*
array(11) {
  [0] => string(7) "0 Value"
  [1] => string(7) "1 Value"
  [2] => string(7) "2 Value"
  [3] => string(7) "3 Value"
  [4] => string(7) "4 Value"
  [5] => string(7) "5 Value"
}
*/

IndexIterator

This iterator counts an independent index during iteration and makes it available. This is useful to count the amount of iterations, mostly. ValueIterator and KeyIterator use this to reset the keys.

use Tale\Iterator\IndexIterator;

$values = new \ArrayIterator(['a' => 'b', 'b' => 'c', 'c' => 'd']);
$indexer = new IndexIterator($values);

foreach ($indexer as $key => $value) {
    $i = $indexer->getIndex();
    echo "{$key} => {$value} - at index: {$i}\n";
}
/*
a => b - at index: 0
b => c - at index: 1
c => d - at index: 2
*/

How to do XYZ?

How to map keys instead of values?

Easy, through chaining a MapIterator and FlipIterators! Notice this doesn't create any additional overhead except for function calls. The internal array is as no point copied or even modified.

use Tale\Iterator\FlipIterator;
use Tale\Iterator\CallbackMapIterator;

$values = new \ArrayIterator(['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4]);
$mapper = new FlipIterator(
    new CallbackMapIterator(
        new FlipIterator($values),
        function (string $key) {
            return "Key {$key}";
        }
    )
);

var_dump(iterator_to_array($mapper));
/*
array(4) {
  'Key a' => int(1)
  'Key b' => int(2)
  'Key c' => int(3)
  'Key d' => int(4)
}
*/

How to filter keys instead of values?

Here, again, the FlipIterator does everything you need!

use Tale\Iterator\FlipIterator;
use Tale\Iterator\CallbackFilterIterator;

$values = new \ArrayIterator(['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4]);
$mapper = new FlipIterator(
    new CallbackFilterIterator(
        new FlipIterator($values),
        function (string $key) {
            return $key !== 'b';
        }
    )
);

var_dump(iterator_to_array($mapper));
/*
array(4) {
  'a' => int(1)
  'c' => int(3)
  'd' => int(4)
}
*/