I have some troubles with an array. I have one array that I want to modify like below. I want to remove element (elements) of it by index and then re-index array. Is it possible?
$foo = array(
'whatever', // [0]
'foo', // [1]
'bar' // [2]
);
$foo2 = array(
'foo', // [0], before [1]
'bar' // [1], before [2]
);
unset($foo[0]); // remove item at index 0
$foo2 = array_values($foo); // 'reindex' array
array_splice($array, 0, 1);
http://php.net/manual/en/function.array-splice.php
You better use array_shift(). That will return the first element of the array, remove it from the array and re-index the array. All in one efficient method.
array_splice($array, array_search(array_value, $array), 1);
2020 Benchmark in PHP 7.4
For these who are not satisfied with current answers, I did a little benchmark script, anyone can run from CLI.
We are going to compare two solutions:
unset() with array_values() VS array_splice().
<?php
echo 'php v' . phpversion() . "\n";
$itemsOne = [];
$itemsTwo = [];
// populate items array with 100k random strings
for ($i = 0; $i < 100000; $i++) {
$itemsOne[] = $itemsTwo[] = sha1(uniqid(true));
}
$start = microtime(true);
for ($i = 0; $i < 10000; $i++) {
unset($itemsOne[$i]);
$itemsOne = array_values($itemsOne);
}
$end = microtime(true);
echo 'unset & array_values: ' . ($end - $start) . 's' . "\n";
$start = microtime(true);
for ($i = 0; $i < 10000; $i++) {
array_splice($itemsTwo, $i, 1);
}
$end = microtime(true);
echo 'array_splice: ' . ($end - $start) . 's' . "\n";
As you can see the idea is simple:
Create two arrays both with the same 100k items (randomly generated strings)
Remove 10k first items from first array using unset() and array_values() to reindex
Remove 10k first items from second array using array_splice()
Measure time for both methods
Output of the script above on my Dell Latitude i7-6600U 2.60GHz x 4 and 15.5GiB RAM:
php v7.4.8
unset & array_values: 29.089932918549s
array_splice: 17.94264793396s
Verdict: array_splice is almost twice more performant than unset and array_values.
So: array_splice is the winner!
Unset($array[0]);
Sort($array);
I don't know why this is being downvoted, but if anyone has bothered to try it, you will notice that it works.
Using sort on an array reassigns the keys of the the array. The only drawback is it sorts the values.
Since the keys will obviously be reassigned, even with array_values, it does not matter is the values are being sorted or not.
Try with:
$foo2 = array_slice($foo, 1);
After some time I will just copy all array elements (excluding these unwanted) to new array
Related
What's the best way to determine the first key in a possibly associative array? My first thought it to just foreach the array and then immediately breaking it, like this:
foreach ($an_array as $key => $val) break;
Thus having $key contain the first key, but this seems inefficient. Does anyone have a better solution?
2019 Update
Starting from PHP 7.3, there is a new built in function called array_key_first() which will retrieve the first key from the given array without resetting the internal pointer. Check out the documentation for more info.
You can use reset and key:
reset($array);
$first_key = key($array);
It's essentially the same as your initial code, but with a little less overhead, and it's more obvious what is happening.
Just remember to call reset, or you may get any of the keys in the array. You can also use end instead of reset to get the last key.
If you wanted the key to get the first value, reset actually returns it:
$first_value = reset($array);
There is one special case to watch out for though (so check the length of the array first):
$arr1 = array(false);
$arr2 = array();
var_dump(reset($arr1) === reset($arr2)); // bool(true)
array_keys returns an array of keys. Take the first entry. Alternatively, you could call reset on the array, and subsequently key. The latter approach is probably slightly faster (Thoug I didn't test it), but it has the side effect of resetting the internal pointer.
Interestingly enough, the foreach loop is actually the most efficient way of doing this.
Since the OP specifically asked about efficiency, it should be pointed out that all the current answers are in fact much less efficient than a foreach.
I did a benchmark on this with php 5.4, and the reset/key pointer method (accepted answer) seems to be about 7 times slower than a foreach. Other approaches manipulating the entire array (array_keys, array_flip) are obviously even slower than that and become much worse when working with a large array.
Foreach is not inefficient at all, feel free to use it!
Edit 2015-03-03:
Benchmark scripts have been requested, I don't have the original ones but made some new tests instead. This time I found the foreach only about twice as fast as reset/key. I used a 100-key array and ran each method a million times to get some noticeable difference, here's code of the simple benchmark:
$array = [];
for($i=0; $i < 100; $i++)
$array["key$i"] = $i;
for($i=0, $start = microtime(true); $i < 1000000; $i++) {
foreach ($array as $firstKey => $firstValue) {
break;
}
}
echo "foreach to get first key and value: " . (microtime(true) - $start) . " seconds <br />";
for($i=0, $start = microtime(true); $i < 1000000; $i++) {
$firstValue = reset($array);
$firstKey = key($array);
}
echo "reset+key to get first key and value: " . (microtime(true) - $start) . " seconds <br />";
for($i=0, $start = microtime(true); $i < 1000000; $i++) {
reset($array);
$firstKey = key($array);
}
echo "reset+key to get first key: " . (microtime(true) - $start) . " seconds <br />";
for($i=0, $start = microtime(true); $i < 1000000; $i++) {
$firstKey = array_keys($array)[0];
}
echo "array_keys to get first key: " . (microtime(true) - $start) . " seconds <br />";
On my php 5.5 this outputs:
foreach to get first key and value: 0.15501809120178 seconds
reset+key to get first key and value: 0.29375791549683 seconds
reset+key to get first key: 0.26421809196472 seconds
array_keys to get first key: 10.059751987457 seconds
reset+key http://3v4l.org/b4DrN/perf#tabs
foreach http://3v4l.org/gRoGD/perf#tabs
key($an_array) will give you the first key
edit per Blixt: you should call reset($array); before key($an_array) to reset the pointer to the beginning of the array.
You could try
array_keys($data)[0]
For 2018+
Starting with PHP 7.3, there is an array_key_first() function that achieve exactly this:
$array = ['foo' => 'lorem', 'bar' => 'ipsum'];
$firstKey = array_key_first($array); // 'foo'
Documentation is available here. 😉
list($firstKey) = array_keys($yourArray);
If efficiency is not that important for you, you can use array_keys($yourArray)[0] in PHP 5.4 (and higher).
Examples:
# 1
$arr = ["my" => "test", "is" => "best"];
echo array_keys($arr)[0] . "\r\n"; // prints "my"
# 2
$arr = ["test", "best"];
echo array_keys($arr)[0] . "\r\n"; // prints "0"
# 3
$arr = [1 => "test", 2 => "best"];
echo array_keys($arr)[0] . "\r\n"; // prints "1"
The advantage over solution:
list($firstKey) = array_keys($yourArray);
is that you can pass array_keys($arr)[0] as a function parameter (i.e. doSomething(array_keys($arr)[0], $otherParameter)).
HTH
Please find the following:
$yourArray = array('first_key'=> 'First', 2, 3, 4, 5);
$keys = array_keys($yourArray);
echo "Key = ".$keys[0];
Working Example:
$myArray = array(
2 => '3th element',
4 => 'first element',
1 => 'second element',
3 => '4th element'
);
echo min(array_keys($myArray)); // return 1
This could also be a solution:
$yourArray = array('first_key'=> 'First', 2, 3, 4, 5);
$first_key = current(array_flip($yourArray));
echo $first_key;
I have tested it and it works.
Working Code.
To enhance on the solution of Webmut, I've added the following solution:
$firstKey = array_keys(array_slice($array, 0, 1, TRUE))[0];
The output for me on PHP 7.1 is:
foreach to get first key and value: 0.048566102981567 seconds
reset+key to get first key and value: 0.11727809906006 seconds
reset+key to get first key: 0.11707186698914 seconds
array_keys to get first key: 0.53917098045349 seconds
array_slice to get first key: 0.2494580745697 seconds
If I do this for an array of size 10000, then the results become
foreach to get first key and value: 0.048488140106201 seconds
reset+key to get first key and value: 0.12659382820129 seconds
reset+key to get first key: 0.12248802185059 seconds
array_slice to get first key: 0.25442600250244 seconds
The array_keys method times out at 30 seconds (with only 1000 elements, the timing for the rest was about the same, but the array_keys method had about 7.5 seconds).
$arr = array('key1'=>'value1','key2'=>'value2','key3'=>'key3');
list($first_key) = each($arr);
print $first_key;
// key1
This is the easier way I had ever found. Fast and only two lines of code :-D
$keys = array_keys($array);
echo $array[$keys[0]];
The best way that worked for me was
array_shift(array_keys($array))
array_keys gets array of keys from initial array and then array_shift cuts from it first element value.
You will need PHP 5.4+ for this.
php73:
$array = ['a' => '..', 'b' => '..'];
array_key_first($array); // 'a'
array_key_last($array); // 'b';
http://php.net/manual/en/function.array-key-first.php
Since PHP 7.3.0 function array_key_first() can be used.
There are several ways to provide this functionality for versions prior to PHP 7.3.0. It is possible to use array_keys(), but that may be rather inefficient. It is also possible to use reset() and key(), but that may change the internal array pointer. An efficient solution, which does not change the internal array pointer, written as polyfill:
<?php
if (!function_exists('array_key_first')) {
function array_key_first(array $arr) {
foreach($arr as $key => $unused) {
return $key;
}
return null;
}
}
?>
Re the #Blixt answer, prior to 7.3.0, this polyfill can be used:
if (!function_exists('array_key_first')) {
function array_key_first(array $array) {
return key(array_slice($array, 0, 1, true));
}
}
This will work on all PHP versions
$firstKey = '' ;
//$contact7formlist - associative array.
if(function_exists('array_key_first')){
$firstKey = array_key_first($contact7formlist);
}else{
foreach ($contact7formlist as $key => $contact7form ){
$firstKey = $key;
break;
}
}
A one-liner:
$array = array('key1'=>'value1','key2'=>'value2','key3'=>'key3');
echo key( array_slice( $array, 0, 1, true ) );
# echos 'key1'
Today I had to search for the first key of my array returned by a POST request. (And note the number for a form id etc)
Well, I've found this:
Return first key of associative array in PHP
http://php.net/key
I've done this, and it work.
$data = $request->request->all();
dump($data);
while ($test = current($data)) {
dump($test);
echo key($data).'<br />';die();
break;
}
Maybe it will eco 15min of an other guy.
CYA.
I think the best and fastest way to do it is:
$first_key=key(array_slice($array, 0, 1, TRUE))
array_chunk split an array into chunks, you can use:
$arr = ['uno'=>'one','due'=>'two','tre'=>'three'];
$firstElement = array_chunk($arr,1,true)[0];
var_dump($firstElement);
You can play with your array
$daysArray = array('Monday', 'Tuesday', 'Sunday');
$day = current($transport); // $day = 'Monday';
$day = next($transport); // $day = 'Tuesday';
$day = current($transport); // $day = 'Tuesday';
$day = prev($transport); // $day = 'Monday';
$day = end($transport); // $day = 'Sunday';
$day = current($transport); // $day = 'Sunday';
To get the first element of array you can use current and for last element you can use end
Edit
Just for the sake for not getting any more down votes for the answer you can convert you key to value using array_keys and use as shown above.
use :
$array = ['po','co','so'];
echo reset($array);
Result : po
I have the following code to pick $n elements from an array $array in PHP:
shuffle($array);
$result = array_splice($array, 0, $n);
Given a large array but only a few elements (for example 5 out of 10000), this is relatively slow, so I would like to optimize it such that not all elements have to be shuffled. The values must be unique.
I'm looking fo the most performant alternative. We can assume that $array has no duplicates and is 0-indexed.
$randomArray = [];
while (count($randomArray) < 5) {
$randomKey = mt_rand(0, count($array)-1);
$randomArray[$randomKey] = $array[$randomKey];
}
This will provide exactly 5 elements with no duplicates and very quickly. The keys will be preserved.
Note: You'd have to make sure $array had 5 or more elements or add some sort of check to prevent an endless loop.
This function performs a shuffle on only $n elements where $n is the number of random elements you want to pick. It will also work on associative arrays and sparse arrays. $array is the array to work on and $n is the number of random elements to retrieve.
If we define the $max_index as count($array) - 1 - $iteration.
It works by generating a random number between 0 and $max_index. Picking the key at that index, and replacing its index with the value at $max_index so that it can never be picked again, as $max_index will be one less at the next iteration and unreachable.
In summary this is the Richard Durstenfeld's Fisher-Yates shuffle but operating only on $n elements instead of the entire array.
function rand_pluck($array, $n) {
$array_keys = array_keys($array);
$array_length = count($array_keys);
$max_index = $array_length -1;
$iterations = min($n, $array_length);
$random_array = array();
while($iterations--) {
$index = mt_rand(0, $max_index);
$value = $array_keys[$index];
$array_keys[$index] = $array_keys[$max_index];
array_push($random_array, $array[$value]);
$max_index--;
}
return $random_array;
}
The trick is to use a variation of shuffle or in other words a partial shuffle.
performance is not the only criterion, statistical efficiency, i.e unbiased sampling is as important (as the original shuffle solution is)
function random_pick( $a, $n )
{
$N = count($a);
$n = min($n, $N);
$picked = array_fill(0, $n, 0); $backup = array_fill(0, $n, 0);
// partially shuffle the array, and generate unbiased selection simultaneously
// this is a variation on fisher-yates-knuth shuffle
for ($i=0; $i<$n; $i++) // O(n) times
{
$selected = mt_rand( 0, --$N ); // unbiased sampling N * N-1 * N-2 * .. * N-n+1
$value = $a[ $selected ];
$a[ $selected ] = $a[ $N ];
$a[ $N ] = $value;
$backup[ $i ] = $selected;
$picked[ $i ] = $value;
}
// restore partially shuffled input array from backup
// optional step, if needed it can be ignored, e.g $a is passed by value, hence copied
for ($i=$n-1; $i>=0; $i--) // O(n) times
{
$selected = $backup[ $i ];
$value = $a[ $N ];
$a[ $N ] = $a[ $selected ];
$a[ $selected ] = $value;
$N++;
}
return $picked;
}
NOTE the algorithm is strictly O(n) in both time and space, produces unbiased selections (it is a partial unbiased shuffling) and produces output which is proper array with consecutive keys (not needing extra array_values etc..)
Use example:
$randomly_picked = random_pick($my_array, 5);
// or if an associative array is used
$randomly_picked_keys = random_pick(array_keys($my_array), 5);
$randomly_picked = array_intersect_key($my_array, array_flip($randomly_picked_keys));
For further variations and extensions of shuffling for PHP:
PHP - shuffle only part of an array
PHP shuffle with seed
How can I take n elements at random from a Perl array?
This will only show benifits for small n compared to an array shuffle, but you could
Choose a random index r n times, each time decreasing the limit by 1
Adjust for previously used indices
Take value
Store used index
Pseudocode
arr = []
used = []
for i = 0..n-1:
r = rand 0..len-i
d = 0
for j = 0..used.length-1:
if r >= used[j]:
d += 1
arr.append($array[r + d])
used.append(r)
return arr
You could generate n-times a random number with mt_rand() and then fill these values in a new array. To go against the case where the same index gets returned twice we use the actual returned index to fill the new array and check always if the index exists in the new array, if so we use while to loop through it as long as we get a duplicate index. At the end we use array_values() to get a 0-indexed array.
$count = count($array) - 1;
$new_array = array();
for($i = 0; $i < $n; $i++) {
$index = mt_rand(0, $count);
while(isset($new_array[$index])) {
$index = mt_rand(0, $count);
}
$new_array[$index] = $array[$index];
}
$new_array = array_values($new_array);
I wonder why everyone here make it so complicated?
Here's the fastest and simplest way:
$randomArray = array_rand(array_flip($array), $n);
I have an array of coordinates that I have extracted from JSON. Only issue I have is each index has a part of each set of coordinates. If this sounds confusing let me explain further. So basically for usage on google maps you have two parts to each set of coordinates usually separated by a comma i.e. 50.192847,-0.837228 (just an example). Problem I've got is somehow the two parts have ended up in different indexes for example:
array[0] = '50.192847'
array[1] = '-0.837228'
array[2] = '53.998772'
array[3] = '2.337622'
I think you get the idea. So my question is how do I combine each pair of indexes to make up each set of coordinates? So again for example combine array[0] and array[1] together. Is there a loop that can do this or a PHP array function of some sort?
Thanks in advance for the help!
Split to pairs and implode with comma
$array[0] = '50.192847';
$array[1] = '-0.837228';
$array[2] = '53.998772';
$array[3] = '2.337622';
foreach (array_chunk($array, 2) as $coords)
echo implode(',', $coords) . "\n";
result
50.192847,-0.837228
53.998772,2.337622
You could use a loop to start at every second key.
$newArray = array();
for($i = 0; $i < count($array) - 1 && count($array) % 2 == 0; $i = $i + 2) {
$newArray[] = $array[$i] . ',' . $array[$i + 1];
}
I have a array of say 50 elements. This array can be of size anything.
I want to have the first 10 elements of the array in a string.
I have the program as:
$array1= array("itself", "aith","Inside","Engineer","cooool","that","it","because");
$i=0;
for($f=0; $f < sizeof(array1); $f++)
{
$temparry = $temparry.array1[$f];
if(($f%10) == 0 && ($f !== 0))
{
$temparray[$i] = $temparray;
$i++;
}
}
==
so that at the end:
I get
temparray1= first 10 elements
temparray2 - next 10 elemnts...
I am not what I am missing in my loops.
After reading your comment, I think you want array_chunk [docs]:
$chunks = array_chunk($array1, 10);
This will create a multidimensional array with each element being an array containing 10 elements.
If you still want to join them to a string, you can use array_map [docs] and implode [docs]:
$strings = array_map('implode', $chunks);
This gives you an array of strings, where each element is the concatenation of a chunk.
This is something you can easily do with array_splice and implode.
Example:
<?php
$array = range(1, 50);
while ( $extracted = array_splice($array, 0, 10) )
{
// You could also assign this to a variable instead of outputting it.
echo implode(' ', $extracted);
}
all you are doing here is creating a temporary value and then deleting it. To save it into a string:
$myArray = array("itself", "aith","Inside","Engineer",
"cooool","that","it","because");
$myString = '';
for($i = 0; $i < 10; $i++) {
$myString .= $myArray[$i];
}
You could also run that inside of another for loop that would run through the entire array giving you ten-element increments.
Actually you can use arrray_slice and implode functions like this:
// put first 10 elements into array output
$output = array_slice($myArray, 10);
// implode the 10 elements into a string
$str = implode("", $output);
OP's fixed code as per comments below:
$array1= array("itself","aith","Inside","Engineer","cooool","that","it","because");
$temparry='';
$temparray = array();
for($f=0; $f < count($array1); $f++)
{
$temparry = $temparry.$array1[$f];
if(($f%3) == 0 && ($f !== 0))
{
$temparray[] = $temparry;
$temparry = '';
}
}
print_r($temparray);
How can I remove an element of an array, and reorder afterwards, without having an empty element in the array?
<?php
$c = array( 0=>12,1=>32 );
unset($c[0]); // will distort the array.
?>
Answer / Solution: array array_values ( array $input ).
<?php
$c = array( 0=>12,1=>32 );
unset($c[0]);
print_r(array_values($c));
// will print: the array cleared
?>
array_values($c)
will return a new array with just the values, indexed linearly.
If you are always removing the first element, then use array_shift() instead of unset().
Otherwise, you should be able to use something like $a = array_values($a).
Another option would be array_splice(). This reorders numeric keys and appears to be a faster method if you are crunching enough data to care. But I like unset() array_values() for readability.
array_splice( $array, $index, $num_elements_to_remove);
http://php.net/manual/en/function.array-splice.php
Speed test:
ArraySplice process used 7468 ms for its computations
ArraySplice spent 918 ms in system calls
UnsetReorder process used 9963 ms for its computations
UnsetReorder spent 31 ms in system calls
Test Code:
function rutime($ru, $rus, $index) {
return ($ru["ru_$index.tv_sec"]*1000 + intval($ru["ru_$index.tv_usec"]/1000))
- ($rus["ru_$index.tv_sec"]*1000 + intval($rus["ru_$index.tv_usec"]/1000));
}
function time_output($title, $rustart, $ru) {
echo $title . " process used " . rutime($ru, $rustart, "utime") .
" ms for its computations\n";
echo $title . " spent " . rutime($ru, $rustart, "stime") .
" ms in system calls\n";
}
$test = array();
for($i = 0; $i<100000; $i++){
$test[$i] = $i;
}
$rustart = getrusage();
for ($i = 0; $i<1000; $i++){
array_splice($test,90000,1);
}
$ru = getrusage();
time_output('ArraySplice', $rustart, $ru);
unset($test);
$test = array();
for($i = 0; $i<100000; $i++){
$test[$i] = $i;
}
$rustart = getrusage();
for ($i = 0; $i<1000; $i++){
unset($test[90000]);
$test = array_values($test);
}
$ru = getrusage();
time_output('UnsetReorder', $rustart, $ru);
If you only remove the first item of the array, you could use array_shift($c);
array_shift() shifts the first value of the array off and returns it, shortening the array by one element and moving everything down. All numerical array keys will be modified to start counting from zero while literal keys won't be touched.
array_shift($stack);
example:
$stack = array("orange", "banana", "apple", "raspberry");
$fruit = array_shift($stack);
print_r($stack);
Output:
Array
(
[0] => banana
[1] => apple
[2] => raspberry
)
Source: http://php.net/manual/en/function.array-shift.php
$array=["one"=>1,"two"=>2,"three"=>3];
$newArray=array_shift($array);
return array_values($newArray);
return [2,3]
array_shift remove first element from an array
array_values return just values
Or reset(); is also a good choice