If I had an array of signed integers e.g:
Array
(
[0] => -3
[1] => 1
[2] => 2
[3] => 3
[4] => 3
)
To get unique values I would instinctively use array_unique but after consideration I could perform array_flip twice which would have the same effect, and I think it would be quicker?
array_unique O(n log n) because of the sort operation it uses
array_flip O(n)
Am I correct in my assumptions?
UPDATE / EXAMPLE:
$intArray1 = array(-4,1,2,3);
print_r($intArray1);
$intArray1 = array_flip($intArray1);
print_r($intArray1);
$intArray1 = array_flip($intArray1);
print_r($intArray1);
Array
(
[0] => -3
[1] => 1
[2] => 2
[3] => 3
[4] => 3
)
Array
(
[-3] => 0
[1] => 1
[2] => 2
[3] => 4
)
Array
(
[0] => -3
[1] => 1
[2] => 2
[4] => 3
)
Source: Tips4all, CCNA FINAL EXAM
I benchmarked it for you: CodePad
ReplyDeleteYour intuition on this was correct!
$test=array();
for($run=0; $run<1000; $run++)
$test[]=rand(0,100);
$time=microtime(true);
for($run=0; $run<100; $run++)
$out=array_unique($test);
$time=microtime(true)-$time;
echo 'Array Unique: '.$time."\n";
$time=microtime(true);
for($run=0; $run<100; $run++)
$out=array_keys(array_flip($test));
$time=microtime(true)-$time;
echo 'Keys Flip: '.$time."\n";
$time=microtime(true);
for($run=0; $run<100; $run++)
$out=array_flip(array_flip($test));
$time=microtime(true)-$time;
echo 'Flip Flip: '.$time."\n";
Output:
Array Unique: 1.1829199790955
Keys Flip: 0.0084578990936279
Flip Flip: 0.0083951950073242
Note that array_keys(array_flip($array)) will give a new key values in order, which in many cases may be what you want (identical except much faster to array_values(array_unique($array))), whereas array_flip(array_flip($array)) is identical (except much faster) to array_unique($array) where the keys remain the same.
Nothing is better than running your own benchmark.
ReplyDelete➜ 8321620 cat first.php
<?php
$arr = array(-3, 1, 2, 3, 3);
for($i = 0; $i <= 1000000; $i++) {
array_unique($arr);
}
➜ 8321620 time php first.php
php first.php 3.24s user 0.01s system 99% cpu 3.251 total
➜ 8321620 cat second.php
<?php
$arr = array(-3, 1, 2, 3, 3);
for($i = 0; $i <= 1000000; $i++) {
array_flip(array_flip($arr));
}
➜ 8321620 time php second.php
php second.php 1.50s user 0.01s system 99% cpu 1.514 total
Update: Array with 1000 elements.
➜ 8321620 cat first.php
<?php
$arr = array();
for($i = 0; $i <= 1000; $i++) {
$arr[] = rand(0, 1000);
}
for($i = 0; $i <= 10000; $i++) {
array_unique($arr);
}
➜ 8321620 time php first.php
php first.php 27.50s user 0.03s system 99% cpu 27.534 total
➜ 8321620 cat second.php
<?php
$arr = array();
for($i = 0; $i <= 1000; $i++) {
$arr[] = rand(0, 1000);
}
for($i = 0; $i <= 10000; $i++) {
array_flip(array_flip($arr));
}
➜ 8321620 time php second.php
php second.php 1.59s user 0.01s system 99% cpu 1.604 total
So yes, your assumption was correct.
you would have to use
ReplyDeletearray_keys( array_flip( $array ) );
which would take more time
I would go for array_unique. It has the added benefit of explaining whats happening.