Filter array by first letter - php

Question

I'm building a platform. Somewhere in my code, there's an array that looks like this (PHP):
$entries = array('p01','p02','g01','g02','a001','a002')
I need to write a script that filters the array based on the first letter. For example, asking for those with the starting letter "p" would give me
$filtered_entries = array('p01','p02');
Similarly, if I asked for those with starting letter "g" or "a" it would give me those as well. Any idea how to accomplish this?

Answer 1

There is an array_filter() function in PHP which you can use to accomplish this:
$filtered = array_filter($array, create_function('$a', 'return $a[0] == "' . $letter . '";'));
I'll leave it to you to generalize the function to handle all the letters.
See: http://www.php.net/manual/en/function.array-filter.php

Answer 2

class FirstCharFilter {
public $char = 'p';
function filter(array $array){
return array_filter($array,array($this,'checkFirstChar'));
}
public function checkFirstChar($a){
return $a[0] == $this->char;
}
}
$filter = new FirstCharFilter();
$filter->char = 'p';
var_dump($filter->filter($array));
$filter->char = 'g';
var_dump($filter->filter($array));
Or if you only need to loop, extend FilterIterator:
class FirstCharIterator extends FilterIterator {
public $char = '';
function accept(){
$string = $this->current();
return is_string($string) && $string[0] == $this->char;
}
}
$iter = new FirstCharIterator(new ArrayIterator($array));
$iter->char = 'p';
foreach($iter as $item) echo $item."\n";

Answer 3

$entries = array('p01','p02','g01','g02','a001','a002');
print_r(
preg_grep('~^p~', $entries) // or preg_grep("~^$letter~",.....
);
http://php.net/manual/en/function.preg-grep.php

Answer 4

function filter_array($array, $letter){
$filtered_array=array();
foreach($array as $key=>$val){
if($val[0]==$letter){
$filtered_array[]=$val;
}
}
return $filtered_array;
}
use it like this to get all p's
$entries = array('p01','p02','g01','g02','a001','a002')
$filtered=filter_array($entries, 'p');

Answer 5

$entries = array('p01','p02','g01','g02','a001','a002');
$filterVar = null;
function filterFunction($v) {
global $filterVar;
if (substr($v,0,1) == $filterVar) {
return $v;
}
}
$filterVar = 'a';
$newEntries = array_filter($entries,'filterFunction');
var_dump($newEntries);

Answer 6

Here's one way of generating filter functions using a closure.
function filter_factory($letter) {
return function ($input) use ($letter) {
return is_string($input) && $input[0] === $letter;
};
}
$entries = array('p01','p02','g01','g02','a001','a002');
$p_entries = array_filter($entries, filter_factory('p'));

Answer 7

This type of solution is much more intuitive and dynamic.
In this example, there are several types of solutions:
Search in the first letters
Sensitive to capital letters
is_array() so if it tends to avoid several errors
<?php
/*
* Search within an asociative array
* Examples:
* $array = array('1_p01','1_P02','2_g01','2_g02','3_a001','3_a002');
* find_in_array($array,'2');
* return: array( 2 => '2_g01',3 => '2_g02')
*
* find_in_array($array,'2',false);
* return: array( 1 => '1_P02')
*
* find_in_array($array,'P0',false,false);
* return: array( 0 => '1_p01',1 => '1_P02')
*
*/
function find_in_array($array, $find='', $FirstChar=true, $CaseInsensitive=true){
if ( is_array($array) ){
return preg_grep("/".($FirstChar ? '^':'')."{$find}/".($CaseInsensitive ? '':'i'), $array);
}
}
$array = array('1_p01','1_P02','2_g01','2_g02','3_a001','3_a002');
$a = find_in_array($array,'2');
var_export($a);
/*
Return:
array (
2 => '2_g01',
3 => '2_g02'
)
*/
$a = find_in_array($array,'P0',false);
var_export($a);
/*
Return:
array (
1 => '1_P02'
)
*/
$a = find_in_array($array,'P0',false,false);
var_export($a);
/*
Return:
array (
0 => '1_p01',
1 => '1_P02'
)
*/