A shorter way to run a match on the array's keys rather than the values:
<?php
function preg_grep_keys($pattern, $input, $flags = 0) {
return array_intersect_key($input, array_flip(preg_grep($pattern, array_keys($input), $flags)));
}
?>
preg_grep
(PHP 4, PHP 5, PHP 7, PHP 8)
preg_grep — Return array entries that match the pattern
Description
Returns the array consisting of the elements of the
array array that match the given
pattern.
Parameters
-
pattern -
The pattern to search for, as a string.
-
array -
The input array.
-
flags -
If set to
PREG_GREP_INVERT, this function returns the elements of the input array that do not match the givenpattern.
Return Values
Returns an array indexed using the keys from the
array array, or false on failure.
Errors/Exceptions
If the regex pattern passed does not compile to a valid regex, an E_WARNING is emitted.
Examples
Example #1 preg_grep() example
<?php
// return all array elements
// containing floating point numbers
$fl_array = preg_grep("/^(\d+)?\.\d+$/", $array);
?>See Also
- PCRE Patterns
- preg_quote() - Quote regular expression characters
- preg_match_all() - Perform a global regular expression match
- preg_filter() - Perform a regular expression search and replace
- preg_last_error() - Returns the error code of the last PCRE regex execution
add a note
User Contributed Notes 4 notes
Daniel Klein ¶
11 years ago
keithbluhm at gmail dot com ¶
14 years ago
Run a match on the array's keys rather than the values:
<?php
function preg_grep_keys( $pattern, $input, $flags = 0 )
{
$keys = preg_grep( $pattern, array_keys( $input ), $flags );
$vals = array();
foreach ( $keys as $key )
{
$vals[$key] = $input[$key];
}
return $vals;
}
?>
amolocaleb at gmail dot com ¶
6 years ago
This may be obvious to most experienced developers,but just in case its not,when using preg_grep to check for whitelisted items ,one must be very careful to explicitly define the regex boundaries or it will fail
<?php
$whitelist = ["home","dashboard","profile","group"];
$possibleUserInputs = ["homd","hom","ashboard","settings","group"];
foreach($possibleUserInputs as $input)
{
if(preg_grep("/$input/i",$whitelist)
{
echo $input." whitelisted";
}else{
echo $input." flawed";
}
}
?>
This results in:
homd flawed
hom whitelisted
ashboard whitelisted
settings flawed
group whitelisted
I think this is because if boundaries are not explicitly defined,preg_grep looks for any instance of the substring in the whole array and returns true if found.This is not what we want,so boundaries must be defined.
<?php
foreach($possibleUserInputs as $input)
{
if(preg_grep("/^$input$/i",$whitelist)
{
echo $input." whitelisted";
}else{
echo $input." flawed";
}
}
?>
this results in:
homd flawed
hom flawed
ashboard flawed
settings flawed
group whitelisted
in_array() will also give the latter results but will require few tweaks if say,the search is to be case insensitive,which is always the case 70% of the time
Timo Klemm ¶
7 years ago
An even shorter way to run a match on the array's keys rather than the values:
<?php
function preg_grep_keys($pattern, $input, $flags = 0) {
return array_flip( preg_grep($pattern, array_flip($input), $flags ) );
}
?>
