Replace whole music notes in string using a "find" array and a "replace" array

Question

I've have a problem with preg_replace() using arrays.

Basically, I'd like to transpose this string:

$string = "Dm F Bb F Am";

To

$New_string = "F#m D D A C#m";

Here is what I do:

$Find = Array("/Dm/", "/F/", "/Bb/", "/Am/", "/Bbm/", "/A/", "/C/");
$Replace = Array('F#m', 'A', 'D', 'C#m', 'Dm', 'C#', 'E');
$New_string = preg_replace($Find, $Replace, $string);

But I get this result instead:

E##m E# D E# E#m

Problem is that every match is replaced by the following, something like this happens (example for E##m):

Dm -> F#m -> A#m -> C##m -> E##m

Is there any solution to simply change Dm to F#m, F to A, etc ?

Looks like a simple str_replace() to me, no preg required — DaveRandom
– DaveRandom, Commented Sep 12, 2012 at 10:21
thanks but I already tried with str_replace() and the result is exactly the same, it's wrong... — SuN
– SuN, Commented Sep 12, 2012 at 10:26
Oh right I see what you're getting at. Will answer in a second. — DaveRandom
– DaveRandom, Commented Sep 12, 2012 at 10:32
I would try to explode the string into an array and replace each item individually in a forEach loop. — Michi
– Michi, Commented Sep 12, 2012 at 10:33

Mihai Iorga · Accepted Answer · 2012-09-12 10:39:42Z

4

You could use strtr():

<?php
    $string = "Dm F Bb F Am";
    $Find = Array('Dm', 'F', 'Bb', 'Am', 'Bbm', 'A', 'C');
    $Replace = Array('F#m', 'A', 'D', 'C#m', 'Dm', 'C#', 'E');

    $New_string = strtr($string, array_combine($Find, $Replace));

    echo $New_string;

    // F#m A D A C#m

answered Sep 12, 2012 at 10:39

Mihai Iorga

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Comments

DaveRandom · Accepted Answer · 2012-09-12 10:47:31Z

preg_replace_callback() is probably the simplest way of doing that, you need to do it in a single operation. Something like this:

<?php

$string = "Dm F Bb F Am";

$replacements = array (
    'Dm' => 'F#m',
    'F' => 'A',
    'Bb' => 'D',
    'Am' => 'C#m',
    'Bbm' => 'Dm',
    'A' => 'C#',
    'C' => 'E'
);

$New_string = preg_replace_callback('/\b('.implode('|', array_map('preg_quote', array_keys($replacements), array_fill(0, count($replacements), '/'))).')\b/', function($match) use($replacements) {
    return $replacements[$match[1]];
}, $string);

echo $New_string;

See it working

Now, I am aware that the code above is a little incomprehensible, so let's break it up a bit and see what each individual component does:

// The input string and a map of search => replace
$string = "Dm F Bb F Am";
$replacements = array (
    'Dm' => 'F#m',
    'F' => 'A',
    'Bb' => 'D',
    'Am' => 'C#m',
    'Bbm' => 'Dm',
    'A' => 'C#',
    'C' => 'E'
);

// Get a list of the search strings only
$searches = array_keys($replacements);

// Fill an array with / characters to the same length as the number of search
// strings. This is required for preg_quote() to work properly
$delims = array_fill(0, count($searches), '/');

// Apply preg_quote() to each search string so it is safe to use in the regex
$quotedSearches = array_map('preg_quote', $searches, $delims);

// Build the regex
$expr = '/\b('.implode('|', $quotedSearches).')\b/';

// Define a callback that will translate search matches to replacements
$callback = function($match) use($replacements) {
  return $replacements[$match[1]];
};

// Do the replacement
$New_string = preg_replace_callback($expr, $callback, $string);

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