array_filter
Finding the longest string in an array?
<?php
function longest_string_in_array($array)
{
$mapping = array_combine($array, array_map('strlen', $array));
return array_keys($mapping, max($mapping));
}
?>
Differences are obvious: returns an array of [i]all[/i] of the longest strings, instead of just picking one arbitrarily. Doesn't do the stripslashing or magic stuff because that's another job for for another function.
array_flip
(PHP 4, PHP 5)
array_flip — 배열 안의 모든 키를 각 키의 연관 값과 교체
설명
array array_flip
( array $trans
)
array_flip()은 뒤집힌 순서의 array를 반환한다. 즉, trans 의 키는 값이 되고, trans 의 값은 키가 된다.
trans 의 값들은 유효한 키가 되어야 한다는 것에 주의한다. 즉, 그 값들은 integer나 string이 될 필요가 있다. 어떤 값이 잘못된 타입을 갖으면 경고메시지가 보일것이다. 그리고 결과적으로 키/값 쌍은 뒤집히지 않을것이다.
같은 값이 여러번 출현하면, 그 값의 제일 마지막 키를 사용할것이고, 나머지 모두 사라지게 될것이다.
인수
- trans
-
뒤집을 키/값 쌍의 배열.
반환값
성공시엔 뒤집은 배열을, 실패시엔 FALSE를 반환합니다.
예제
Example #1 array_flip() 예제
<?php
$trans = array_flip($trans);
$original = strtr($str, $trans);
?>
Example #2 array_flip() 예제 : 충돌
<?php
$trans = array("a" => 1, "b" => 1, "c" => 2);
$trans = array_flip($trans);
print_r($trans);
?>
이제 $trans는:
Array
(
[1] => b
[2] => c
)
add a note
User Contributed Notesarray_flip
Hayley Watson
20-Mar-2009 10:22
20-Mar-2009 10:22
dan at aoindustries dot com
07-Mar-2009 08:48
07-Mar-2009 08:48
From an algorithmic efficiency standpoint, building an entire array of lengths to then sort to only retrieve the longest value is unnecessary work. The following should be O(n) instead of O(n log n). It could also be:
<?php
function get_longest_value($array) {
// Some don't like to initialize, I do
$longest = NULL;
$longestLen = -1;
foreach ($array $value) {
$len = strlen($value);
if($len>$longestLen) {
$longest = $value;
$longestLen = $len;
}
}
$longest = str_replace("\r\n", "\n", $longest);
if (get_magic_quotes_gpc()) { return stripslashes($longest); }
return $longest;
}
?>
corz at corz dot org
08-Dec-2008 09:36
08-Dec-2008 09:36
<?php
/*
Fun function to return the longest physical *value* from an array.
Culled from a small script designed to capture the longest $_POST variable,
usually the textarea, which would then be dumped to a "emergency post dump file".
corz at corz dot org
*/
$array = array("input" => "submit", "textarea" => "Some long spiel of text\r\na textarea, probably",
"another-input" => "make me longer", "and" => "another", "etc" => "etc.");
echo '<!DOCTYPE HTML SYSTEM><html><head><title>long</title></head><body><pre>Longest value: ',
get_longest_value($array),'</pre></body></html>';
function get_longest_value($array) {
foreach ($array as $key => $value) {
$lengths[$key] = strlen($value);
}
asort($lengths);
$lengths = array_flip($lengths);
$longest = str_replace("\r\n", "\n", $array[array_pop($lengths)]);
if (get_magic_quotes_gpc()) { return stripslashes($longest); }
return $longest;
}
?>
rdanner
21-Aug-2008 01:17
21-Aug-2008 01:17
using array_flip(array_flip($array)) or array_keys(array_flip($array)) as key-collapsing alternatives to array_unique() makes your intention less apparent. Try:
array_values(array_unique($array))
as a more readable alternative.
Anonymous
29-Feb-2008 07:45
29-Feb-2008 07:45
True, array_unique does preserve keys, but if you are incrementing in a loop, then it will stop once the key values break numerical order. If you don't care about preserving keys, a life-saver (originally a headache) for me was...
<?php
$new_array = array_keys(array_flip($old_array));
?>
i used this little snip-it after results from preg_match_all() as a way to remove duplicates from an array and then re-organize the numerical keys ;)
*Only works on arrays with numerical keys.
eSeYaRr
28-Aug-2007 04:21
28-Aug-2007 04:21
In array_unique() user notes, you'll see that the flip flip use is faster than the array_unique() use for that purpose.
pinkgothic at gmail dot com
26-Apr-2007 08:37
26-Apr-2007 08:37
In case anyone is wondering how array_flip() treats empty arrays:
<?php
print_r(array_flip(array()));
?>
results in:
Array
(
)
I wanted to know if it would return false and/or even chuck out an error if there were no key-value pairs to flip, despite being non-intuitive if that were the case. But (of course) everything works as expected. Just a head's up for the paranoid.
http://www.callum-macdonald.com/
06-Mar-2007 06:13
06-Mar-2007 06:13
It might seem obvious, but if you want to remove duplicates from an array, you can use array_flip() twice:
$arr = array_flip(array_flip($arr));
mikeb at tracersinfo dot com
06-Feb-2006 10:42
06-Feb-2006 10:42
Further deriving on benles -> crescentfreshpot, I think the following restatement of array_invert() reads much easier and probably runs faster, too. It does yield the same results:
function array_invert($arr) {
$flipped = array();
foreach ( $arr as $k => $a ) {
# put the value in the key, with a throw-away value. dups are inherently avoided,
# though overwritten. not sure if prefixing with if ( !isset($flipped[$a][$k]) )
# would speed this up or slow it down. probably depends on quantity of dups.
$flipped[$a][$k] = NULL;
}
foreach ( $flipped as $k => $fl ) {
# now make the keys the values.
$flipped[$k] = array_keys($fl);
}
return $flipped;
}
crescentfreshpot at yahoo dot com
03-Jul-2005 11:21
03-Jul-2005 11:21
Furthering benles note, if you don't want duplicate values to overwrite existing keys but need non-duplicate values to be assigned like array_flip, use:
<?php
function array_invert($arr)
{
$flipped = array();
foreach(array_keys($arr) as $key) {
if(array_key_exists($arr[$key],$flipped)) {
$flipped[$arr[$key]] = array_merge((array)$flipped[$arr[$key]], (array)$key);
} else {
$flipped[$arr[$key]] = $key;
}
}
return $flipped;
}
$a = array(
'orange' => 'fruit',
'milk' => 'dairy',
'apple' => 'fruit',
'banana' => 'fruit'
);
print_r(array_invert($a));
/*
Output:
Array
(
[fruit] => Array
(
[0] => orange
[1] => apple
[2] => banana
)
[dairy] => milk
)
*/
?>
benles at bldigital dot com
06-Mar-2005 01:52
06-Mar-2005 01:52
In case anyone wants a function that doesn't lose duplicates:
function array_invert($arr)
{
$res = Array();
foreach(array_keys($arr) as $key)
{
if (!array_key_exists($arr[$key], $res)) $res[$arr[$key]] = Array();
array_push($res[$arr[$key]], $key);
}
return $res;
}
snaury at narod dot ru
23-Nov-2004 07:21
23-Nov-2004 07:21
When you do array_flip, it takes the last key accurence for each value, but be aware that keys order in flipped array will be in the order, values were first seen in original array. For example, array:
[1] => 1
[2] => 2
[3] => 3
[4] => 3
[5] => 2
[6] => 1
[7] => 1
[8] => 3
[9] => 3
After flipping will become:
(first seen value -> first key)
[1] => 7
[2] => 5
[3] => 9
And not anything like this:
(last seen value -> last key)
[2] => 5
[1] => 7
[3] => 9
In my application I needed to find five most recently commented entries. I had a sorted comment-id => entry-id array, and what popped in my mind is just do array_flip($array), and I thought I now would have last five entries in the array as most recently commented entry => comment pairs. In fact it wasn't (see above, as it is the order of values used). To achieve what I need I came up with the following (in case someone will need to do something like that):
First, we need a way to flip an array, taking the first encountered key for each of values in array. You can do it with:
$array = array_flip(array_unique($array));
Well, and to achieve that "last comments" effect, just do:
$array = array_reverse($array, true);
$array = array_flip(array_unique($array));
$array = array_reverse($array, true);
In the example from the very beginning array will become:
[2] => 5
[1] => 7
[3] => 9
Just what I (and maybe you?) need. =^_^=
znailz at yahoo dot com
05-Aug-2003 09:42
05-Aug-2003 09:42
I know a lot of people want a function to remove a key by value from an array. I saw solutions that iterate(!) though the whole array comparing value by value and then unsetting that value's key. PHP has a built-in function for pretty much everything (heard it will even cook you breakfast), so if you think "wouldn't it be cool if PHP had a function to do that...", odds are it already has. Check out this example. It takes a value, gets all keys for that value if it has duplicates, unsets them all, and returns a reindexed array.
<?php
$arr = array(11,12,13,12); // sample array
$arr = array_flip($arr);
unset($arr[12]);
$arr = array(array_keys($arr));
?>
$arr contains:
<?php
Array
(
[0] => Array
(
[0] => 11
[1] => 13
)
?>
)