PHP Better way to Replace/Match $1 - php

Question

I am trying to replace $1, $2, $3 variables in a URL with another URL.
You can copy paste my example below and see my solution.
But I feel like there is a more elegant way with an array mapping type function or a better preg_replace type of thing. I just need a kick in the right direction, can you help?
<?php
/**
* Key = The DESIRED string
* Value = The ORIGINAL value
*
* Desired Result: project/EXAMPLE/something/OTHER
*/
$data = array(
'project/$1/details/$2' => 'newby/EXAMPLE/something/OTHER'
);
foreach($data as $desiredString => $findMe)
{
/**
* Turn these URI's into arrays
*/
$desiredString = explode('/', $desiredString);
$findMe = explode('/', $findMe);
/**
* Store the array position of the match
*/
$positions = array();
foreach($desiredString as $key => $value) {
/**
* Look for $1, $2, $3, etc..
*/
if (preg_match('#(\$\d)#', $value)) {
$positions[$key] = $value;
}
}
/**
* Loop through the positions
*/
foreach($positions as $key => $value){
$desiredString[$key] = $findMe[$key];
}
/**
* The final result
*/
echo implode('/', $desiredString);
}

Answer 1

Sometimes you are out of luck and the functions you need to solve a problem directly just aren't there. This happens with every language regardless of how many libraries and builtins it has.
We're going to have to write some code. We also need to solve a particular problem. Ultimately, we want our solution to the problem to be just as clean as if we had the ideal functions given to us in the first place. Therefore, whatever code we write, we want most of it to be out of the way, which probably means we want most of the code in a separate function or class. But we don't just want to just throw around arbitrary code because all of our functions and classes should be reusable.
My approach then is to extract a useful general pattern out of the solution, write that as a function, and then rewrite the original solution using that function (which will simplify it). To find that general pattern I made the problem bigger so it might be applicable to more situations.
I ended up making the function array array_multi_walk(callback $callback [, array $array1 [, array $array2 ... ]]). This function walks over each array simultaneously and uses $callback to select which element to keep.
This is what the solution looks like using this function.
$chooser = function($a, $b) {
return strlen($a) >= 2 && $a[0] == '$' && ctype_digit($a[1])
? $b : $a;
};
$data = array(
'project/$1/details/$2' => 'newby/EXAMPLE/something/OTHER'
);
$explodeSlashes = function($a) { return explode('/', $a); };
$find = array_map($explodeSlashes, array_keys($data));
$replace = array_map($explodeSlashes, array_values($data));
$solution = array_multi_walk(
function($f, $r) use ($chooser) {
return array_multi_walk($chooser, $f, $r);
},
$find, $replace);
And, as desired, array_multi_walk can be used for other problems. For example, this sums all elements.
$sum = function() {
return array_sum(func_get_args());
};
var_dump(array_multi_walk($sum, array(1,2,3), array(1,2,3), array(10)));
// prints the array (12, 4, 6)
You might want to make some tweaks to array_multi_walk. For example, it might be better if the callback takes the elements by array, rather than separate arguments. Maybe there should be option flags to stop when any array runs out of elements, instead of filling nulls.
Here is the implementation of array_multi_walk that I came up with.
function array_multi_walk($callback)
{
$arrays = array_slice(func_get_args(), 1);
$numArrays = count($arrays);
if (count($arrays) == 0) return array();
$result = array();
for ($i = 0; ; ++$i) {
$elementsAti = array();
$allNull = true;
for ($j = 0; $j < $numArrays; ++$j) {
$element = array_key_exists($i, $arrays[$j]) ? $arrays[$j][$i] : null;
$elementsAti[] = $element;
$allNull = $allNull && $element === null;
}
if ($allNull) break;
$result[] = call_user_func_array($callback, $elementsAti);
}
return $result;
}
So at the end of the day, we had to write some code, but not only is the solution to the original problem slick, we also gained a generic, reusable piece of code to help us out later.

Answer 2

Why there should not be $2,$4 but $1,$2 ?if you can change your array then it can be solved in 3 or 4 lines codes.
$data = array(
'project/$2/details/$4' => 'newby/EXAMPLE/something/OTHER'
);
foreach($data as $desiredString => $findMe)
{
$regexp = "#(".implode(')/(',explode('/',$findMe)).")#i";
echo preg_replace($regexp,$desiredString,$findMe);
}

Answer 3

I've shortened your code by removing comments for better readability. I'm using array_map and the mapping function decides what value to return:
<?php
function replaceDollarSigns($desired, $replace)
{
return preg_match('#(\$\d)#', $desired) ? $replace : $desired;
}
$data = array(
'project/$1/details/$2' => 'newby/EXAMPLE/something/OTHER',
);
foreach($data as $desiredString => $findMe)
{
$desiredString = explode('/', $desiredString);
$findMe = explode('/', $findMe);
var_dump(implode('/', array_map('replaceDollarSigns', $desiredString, $findMe)));
}
?>
Working example: http://ideone.com/qVLmn
You can also omit the function by using create_function:
<?php
$data = array(
'project/$1/details/$2' => 'newby/EXAMPLE/something/OTHER',
);
foreach($data as $desiredString => $findMe)
{
$desiredString = explode('/', $desiredString);
$findMe = explode('/', $findMe);
$result = array_map(
create_function(
'$desired, $replace',
'return preg_match(\'#(\$\d)#\', $desired) ? $replace : $desired;'
),
$desiredString,
$findMe);
var_dump(implode('/', $result));
}
?>
Working example: http://ideone.com/OC0Ak

Answer 4

Just saying, why don't use an array pattern/replacement in preg_replace? Something like this:
<?php
/**
* Key = The DESIRED string
* Value = The ORIGINAL value
*
* Desired Result: project/EXAMPLE/something/OTHER
*/
$data = array(
'project/$1/details/$2' => 'newby/EXAMPLE/details/OTHER'
);
$string = 'project/$1/details/$2';
$pattern[0] = '/\$1/';
$pattern[1] = '/\$2/';
$replacement[0] = 'EXAMPLE';
$replacement[1] = 'OTHER';
$result = preg_replace($pattern, $replacement, $string);
echo $result;
I think that it's much easier than what you're looking for. You can see that it works here: http://codepad.org/rCslRmgs
Perhaps there's some reason to keep the array key => value to accomplish the replace?