I am searching for a built in php function that takes array of keys as input and returns me corresponding values.
for e.g. I have a following array
$arr = array("key1"=>100, "key2"=>200, "key3"=>300, 'key4'=>400);
and I need values for the keys key2 and key4 so I have another array("key2", "key4")
I need a function that takes this array and first array as inputs and provide me values in response. So response will be array(200, 400)
I think you are searching for array_intersect_key. Example:
array_intersect_key(array('a' => 1, 'b' => 3, 'c' => 5),
array_flip(array('a', 'c')));
Would return:
array('a' => 1, 'c' => 5);
You may use array('a' => '', 'c' => '') instead of array_flip(...) if you want to have a little simpler code.
Note the array keys are preserved. You should use array_values afterwards if you need a sequential array.
An alternative answer:
$keys = array("key2", "key4");
return array_map(function($x) use ($arr) { return $arr[$x]; }, $keys);
foreach($input_arr as $key) {
$output_arr[] = $mapping[$key];
}
This will result in $output_arr having the values corresponding to a list of keys in $input_arr, based on the key->value mapping in $mapping. If you want, you could wrap it in a function:
function get_values_for_keys($mapping, $keys) {
foreach($keys as $key) {
$output_arr[] = $mapping[$key];
}
return $output_arr;
}
Then you would just call it like so:
$a = array('a' => 1, 'b' => 2, 'c' => 3);
$values = get_values_for_keys($a, array('a', 'c'));
// $values is now array(1, 3)
Related
I have an array as the following:
function example() {
/* some stuff here that pushes items with
dynamically created key strings into an array */
return array( // now lets pretend it returns the created array
'firstStringName' => $whatEver,
'secondStringName' => $somethingElse
);
}
$arr = example();
// now I know that $arr contains $arr['firstStringName'];
I need to find out the index of $arr['firstStringName'] so that I am able to loop through array_keys($arr) and return the key string 'firstStringName' by its index. How can I do that?
If you have a value and want to find the key, use array_search() like this:
$arr = array ('first' => 'a', 'second' => 'b', );
$key = array_search ('a', $arr);
$key will now contain the key for value 'a' (that is, 'first').
key($arr);
will return the key value for the current array element
http://uk.php.net/manual/en/function.key.php
If i understand correctly, can't you simply use:
foreach($arr as $key=>$value)
{
echo $key;
}
See PHP manual
If the name's dynamic, then you must have something like
$arr[$key]
which'd mean that $key contains the value of the key.
You can use array_keys() to get ALL the keys of an array, e.g.
$arr = array('a' => 'b', 'c' => 'd')
$x = array_keys($arr);
would give you
$x = array(0 => 'a', 1 => 'c');
Here is another option
$array = [1=>'one', 2=>'two', 3=>'there'];
$array = array_flip($array);
echo $array['one'];
Yes you can infact php is one of the few languages who provide such support..
foreach($arr as $key=>$value)
{
}
if you need to return an array elements with same value, use array_keys() function
$array = array('red' => 1, 'blue' => 1, 'green' => 2);
print_r(array_keys($array, 1));
use array_keys() to get an array of all the unique keys.
Note that an array with named keys like your $arr can also be accessed with numeric indexes, like $arr[0].
http://php.net/manual/en/function.array-keys.php
you can use key function of php to get the key name:
<?php
$array = array(
'fruit1' => 'apple',
'fruit2' => 'orange',
'fruit3' => 'grape',
'fruit4' => 'apple',
'fruit5' => 'apple');
// this cycle echoes all associative array
// key where value equals "apple"
while ($fruit_name = current($array)) {
if ($fruit_name == 'apple') {
echo key($array).'<br />';
}
next($array);
}
?>
like here : PHP:key - Manual
So I have an associative array and I want to return 2 random values from it.
This code only returns 1 array value, which is any of the 4 numbers at random.
$array = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4);
$key = array_rand($array); //array_rand($array,2); Putting 2 returns Illegal offset type
$value = $array[$key];
print_r($value); //prints a single random value (ex. 3)
How can I return 2 comma separated values from the array values only? Something like 3,4?
array_rand takes an additional optional parameter which specifies how many random entries you want out of the array.
$input_array = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4);
$rand_keys = array_rand($input_array, 2);
echo $input_array[$rand_keys[0]] . ',' . $input_array[$rand_keys[1]];
Check the PHP documentation for array_rand here.
Grab the keys from the array with array_keys(), shuffle the keys with shuffle(), and print out the values corresponding to the first two keys in the shuffled keys array, like so:
$array = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4);
$keys = array_keys( $array);
shuffle( $keys);
echo $array[ $keys[0] ] . ',' . $array[ $keys[1] ];
Demo
Or, you can use array_rand()'s second parameter to grab two keys, like so:
$array = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4);
$keys = array_rand( $array, 2);
echo $array[ $keys[0] ] . ',' . $array[ $keys[1] ];
Demo
There is a more efficient approach that preserves keys and values.
function shuffle_assoc(&$array) {
$keys = array_keys($array);
shuffle($keys);
foreach($keys as $key) {
$new[$key] = $array[$key];
}
$array = $new;
return true;
}
Check the documentation here
$a=rand(0,sizeof($array));
$b=$a;
while ($a==$b) $b=rand(0,sizeof($array));
$ar=array_values($array);
$element1=$ar[$a];
$element2=$ar[$b];
Should be more efficient than shuffle() and freinds, if the array is large.
I have an array with keys and values. Each value is an integer. I have an other array with the same keys. How can I subtract all of the values for the matching keys? Also there might be keys that do not occur in the second array but both arrays have the same length. If there is a key in array 2 that is not present in array 1 its value should be unchanged. If there is a key in the first array that is not in the second it should be thrown away. How do I do it? Is there any built-in function for this?
If I would write a script it would be some kind of for loop like this:
$arr1 = array('a' => 1, 'b' => 3, 'c' => 10);
$arr2 = array('a' => 2, 'b' => 1, 'c' => 5);
$ret = array();
foreach ($arr1 as $key => $value) {
$ret[$key] = $arr2[$key] - $arr1[$key];
}
print_r($ret);
/*
should be: array('a' => 1, 'b' => -2, 'c' => -5)
*/
I did not add the occasion here a key is in one array and not in the other.
You could avoid the foreach using array functions if you were so inclined.
The closure provided to array_mapdocs below will subtract each $arr1 value from each corresponding $arr2. Unfortunately array_map won't preserve your keys when using more than one input array, so we use array_combinedocs to merge the subtracted results back into an array with the original keys:
$arr1 = array('a' => 1, 'b' => 3, 'c' => 10);
$arr2 = array('a' => 2, 'b' => 1, 'c' => 5);
$subtracted = array_map(function ($x, $y) { return $y-$x; } , $arr1, $arr2);
$result = array_combine(array_keys($arr1), $subtracted);
var_dump($result);
UPDATE
I was interested in how the array functions approach compared to a simple foreach, so I benchmarked both using Xdebug. Here's the test code:
$arr1 = array('a' => 1, 'b' => 3, 'c' => 10);
$arr2 = array('a' => 2, 'b' => 1, 'c' => 5);
function arrayFunc($arr1, $arr2) {
$subtracted = array_map(function ($x, $y) { return $y-$x; } , $arr1, $arr2);
$result = array_combine(array_keys($arr1), $subtracted);
}
function foreachFunc($arr1, $arr2) {
$ret = array();
foreach ($arr1 as $key => $value) {
$ret[$key] = $arr2[$key] - $arr1[$key];
}
}
for ($i=0;$i<10000;$i++) { arrayFunc($arr1, $arr2); }
for ($i=0;$i<10000;$i++) { foreachFunc($arr1, $arr2); }
As it turns out, using the foreach loop is an order of magnitude faster than accomplishing the same task using array functions. As you can see from the below KCachegrind callee image, the array function method required nearly 80% of the processing time in the above code, while the foreach function required less than 5%.
The lesson here: sometimes the more semantic array functions (surprisingly?) can be inferior performance-wise to a good old fashioned loop in PHP. Of course, you should always choose the option that is more readable/semantic; micro-optimizations like this aren't justified if they make the code more difficult to understand six months down the road.
foreach ($arr2 as $key => $value) {
if(array_key_exists($key, $arr1) && array_key_exists($key, $arr2))
$ret[$key] = $arr2[$key] - $arr1[$key];
}
PHP does not offer vectorized mathematical operations. I would stick with your current approach of using a loop.
First, I would get the set of array keys for each array. (See the array_keys function). Then, intersect them. Now you will have the keys common to each array. (Take a look at the array_intersect function). Finally, iterate. It's a readable and simple approach.
Lastly, you could take a look at a library, such as Math_Vector: http://pear.php.net/package/Math_Vector
I have an array as the following:
function example() {
/* some stuff here that pushes items with
dynamically created key strings into an array */
return array( // now lets pretend it returns the created array
'firstStringName' => $whatEver,
'secondStringName' => $somethingElse
);
}
$arr = example();
// now I know that $arr contains $arr['firstStringName'];
I need to find out the index of $arr['firstStringName'] so that I am able to loop through array_keys($arr) and return the key string 'firstStringName' by its index. How can I do that?
If you have a value and want to find the key, use array_search() like this:
$arr = array ('first' => 'a', 'second' => 'b', );
$key = array_search ('a', $arr);
$key will now contain the key for value 'a' (that is, 'first').
key($arr);
will return the key value for the current array element
http://uk.php.net/manual/en/function.key.php
If i understand correctly, can't you simply use:
foreach($arr as $key=>$value)
{
echo $key;
}
See PHP manual
If the name's dynamic, then you must have something like
$arr[$key]
which'd mean that $key contains the value of the key.
You can use array_keys() to get ALL the keys of an array, e.g.
$arr = array('a' => 'b', 'c' => 'd')
$x = array_keys($arr);
would give you
$x = array(0 => 'a', 1 => 'c');
Here is another option
$array = [1=>'one', 2=>'two', 3=>'there'];
$array = array_flip($array);
echo $array['one'];
Yes you can infact php is one of the few languages who provide such support..
foreach($arr as $key=>$value)
{
}
if you need to return an array elements with same value, use array_keys() function
$array = array('red' => 1, 'blue' => 1, 'green' => 2);
print_r(array_keys($array, 1));
use array_keys() to get an array of all the unique keys.
Note that an array with named keys like your $arr can also be accessed with numeric indexes, like $arr[0].
http://php.net/manual/en/function.array-keys.php
you can use key function of php to get the key name:
<?php
$array = array(
'fruit1' => 'apple',
'fruit2' => 'orange',
'fruit3' => 'grape',
'fruit4' => 'apple',
'fruit5' => 'apple');
// this cycle echoes all associative array
// key where value equals "apple"
while ($fruit_name = current($array)) {
if ($fruit_name == 'apple') {
echo key($array).'<br />';
}
next($array);
}
?>
like here : PHP:key - Manual
I am searching for a built in php function that takes array of keys as input and returns me corresponding values.
for e.g. I have a following array
$arr = array("key1"=>100, "key2"=>200, "key3"=>300, 'key4'=>400);
and I need values for the keys key2 and key4 so I have another array("key2", "key4")
I need a function that takes this array and first array as inputs and provide me values in response. So response will be array(200, 400)
I think you are searching for array_intersect_key. Example:
array_intersect_key(array('a' => 1, 'b' => 3, 'c' => 5),
array_flip(array('a', 'c')));
Would return:
array('a' => 1, 'c' => 5);
You may use array('a' => '', 'c' => '') instead of array_flip(...) if you want to have a little simpler code.
Note the array keys are preserved. You should use array_values afterwards if you need a sequential array.
An alternative answer:
$keys = array("key2", "key4");
return array_map(function($x) use ($arr) { return $arr[$x]; }, $keys);
foreach($input_arr as $key) {
$output_arr[] = $mapping[$key];
}
This will result in $output_arr having the values corresponding to a list of keys in $input_arr, based on the key->value mapping in $mapping. If you want, you could wrap it in a function:
function get_values_for_keys($mapping, $keys) {
foreach($keys as $key) {
$output_arr[] = $mapping[$key];
}
return $output_arr;
}
Then you would just call it like so:
$a = array('a' => 1, 'b' => 2, 'c' => 3);
$values = get_values_for_keys($a, array('a', 'c'));
// $values is now array(1, 3)