foreach ($array as $value) { // Act on $value }
Or, to get an array’s keys and values:
foreach ($array as $key => $value) { // Act II }
Another technique is to use
for
:
for ($key = 0, $size = count($array); $key < $size; $key++) { // Act III }
Finally, you can use
each( )
in
combination with list( )
and
while
:
reset($array) // reset internal pointer to beginning of array while (list($key, $value) = each ($array)) { // Final Act }
A foreach
loop is the shortest way to iterate
through an array:
// foreach with values foreach ($items as $cost) { ... } // foreach with keys and values foreach($items as $item => $cost) { ... }
With foreach
, PHP iterates over a copy of the
array instead of the actual array. In contrast, when using
each( )
and for
, PHP iterates
over the original array. So, if you modify the array inside the loop,
you may (or may not) get the behavior you expect.
If you want to modify the array, reference it directly:
reset($items); while (list($item, $cost) = each($items)) { if (! in_stock($item)) { unset($items[$item]); // address the array directly } }
The variables returned by each( )
aren’t aliases for the original values in the array:
they’re copies, so, if you modify them,
it’s not reflected in the array.
That’s why you need to modify
$items[$item]
instead of $item
.
When using each( )
, PHP keeps track of where you
are inside the loop. After completing a first pass through, to begin
again at the start, call reset( )
to move the
pointer back to the front of the array. Otherwise, each( )
returns false
.
The for
loop works only for arrays with
consecutive integer keys. Unless you’re modifying
the size of your array, it’s inefficient to
recompute the count( )
of
$items
each time through the loop, so we always
use a $size
variable to hold the
array’s size:
for ($item = 0, $size = count($items); $item < $size; $item++) { ... }
If you prefer to count efficiently with one variable, count backwards:
for ($item = count($items) - 1; $item >= 0; $item--) { ... }
The associative version of the
for
loop is:
for (reset($array); $key = key($array); next($array) ) { ... }
This fails if any element holds a string that evaluates to
false
, so a perfectly normal value such as 0
causes the loop to end early.
Finally, use array_map( )
to hand off
each element to a function for processing:
// lowercase all words $lc = array_map('strtolower', $words);
The first argument to array_map( )
is a function
to modify an individual element, and the second is the array to be
iterated through.
Generally, we find these functions less flexible than the previous methods, but they are well-suited for the processing and merging of multiple arrays.
If you’re unsure
if the data you’ll be processing is a
scalar or an array, you need to protect
against calling foreach
with a non-array. One
method is to use is_array( )
:
if (is_array($items)) { // foreach loop code for array } else { // code for scalar }
Another method is to coerce all variables into array form using
settype( )
:
settype($items, 'array'); // loop code for arrays
This turns a scalar value into a one element array and cleans up your code at the expense of a little overhead.
Documentation on for
at
http://www.php.net/for,
foreach
at
http://www.php.net/foreach,
while
at
http://www.php.net/while, each( )
at http://www.php.net/each,
reset( )
at
http://www.php.net/reset, and
array_map( )
at
http://www.php.net/array-map.
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