Does PHP have an equivalent to Python's list c

问题:

Python has syntactically sweet list comprehensions:

S = [x**2 for x in range(10)]
print S;
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

In PHP I would need to do some looping:

$output = array();
$Nums = range(0,9);

foreach ($Nums as $num) 
{
    $out[] = $num*=$num;
}
print_r($out);

to get:

Array ( [0] => 0 [1] => 1 [2] => 4 [3] => 9 [4] => 16 [5] => 25 [6] => 36 [7] => 49 [8] => 64 [9] => 81 )

Is there anyway to get a similar list comprehension syntax in PHP? Is there anyway to do it with any of the new features in PHP 5.3?

Thanks!

回答1:

Maybe something like this?

$out=array_map(function($x) {return $x*$x;}, range(0, 9))

This will work in PHP 5.3+, in an older version you'd have to define the callback for array_map separately

function sq($x) {return $x*$x;}
$out=array_map('sq', range(0, 9));

回答2:

PHP 5.5 may support list comprehensions - see the mailing list announcement:

• [PHP-DEV] List comprehensions and generator expressions for PHP (28 Jun 2012)

And further discussion:

• What Generators Can Do For You (by ircmaxell; 23 Jul 2012) - has a Fibonacci example.
• What PHP 5.5 might look like (by NikiC; 10 Jul 2012)
• Request for Comments: Generators (Wiki started 05 Jun 2012)

回答3:

not out of the box, but take a look at: http://code.google.com/p/php-lc/ or http://code.google.com/p/phparrayplus/

回答4:

In .NET, the equivalent of Python's "syntactically sweet list comprehensions" is LINQ. And in PHP, there're several ports of it, including YaLinqo library*. Syntactically, it's closer to SQL rather than a sequence of traditional constructs with for and if, but functionally, it's similar:

$a = Enumerable::range(0, 10)->select('$v * $v');

This produces an iterator which can either be output to console:

var_dump($a->toArray()); // by transforming the iterator to an array
echo $a->toString(', '); // or by imploding into a string

or iterated over using foreach:

foreach ($a as $i)
    echo $i, PHP_EOL;

Here, '$v * $v' is a shortcut for function ($v) { return $v * $v; } which this library supports. Unfortunately, PHP doesn't support short syntax for closures, but such "string lambdas" can be used to make the code shorter.

There're many more methods, starting with where (if equivalent) and ending with groupJoin which performs joining transformation with grouping.

_{* developed by me}