Find and Replace Multi-Row Phrases/text Within PHP Arrays without damaging the array

Lets say I have an array:

$myarray = (
 [0] => 'Johnny likes to go to school',
 [1] => 'but he only likes to go on Saturday',
 [2] => 'because Saturdays are the best days', 
 [3] => 'unless you of course include Sundays',
 [4] => 'which are also pretty good days too.',
 [5] => 'Sometimes Johnny likes picking Strawberrys',
 [6] => 'with his mother in the fields',
 [7] => 'but sometimes he likes picking blueberries'
);

Keeping the structure of this array intact, I want to be able to replace phrases within it, even if they spill over to the next or previous string. Also I don’t want punctuation or case to impact it.

Examples:

String to Find: “Sundays which are also pretty good”

Replace with: “Mondays which are also pretty great”

After replace:

$myarray = (
     [0] => 'Johnny likes to go to school',
     [1] => 'but he only likes to go on Saturday',
     [2] => 'because Saturdays are the best days', 
     [3] => 'unless you of course include Mondays', 
     [4] => 'which are also pretty great days too.',
     [5] => 'Sometimes Johnny likes picking Strawberrys',
     [6] => 'with his mother in the fields',
     [7] => 'but sometimes he likes picking blueberries'
    );

Curious if there is an ideal way of doing this. My original thought was, I would turn the array into a string, strip out punctuation and spaces, count the characters and replace the phrase based on the character count. But, it is getting rather complex, but it is a complex problem

Answer

This is a job for regular expressions.

The method I used was to implode the array with some glue (i.e. '&'). Then I generated a regular expression by inserting a zero-or-one check for '&' in between each character in the find string.

I used the regular expression to replace occurrences of the string we were looking for with the replacement string. Then I exploded the string back into an array using the same delimiter as above ('&')

$myarray = [
    0 => 'Johnny likes to go to school',
    1 => 'but he only likes to go on Saturday',
    2 => 'because Saturdays are the best days',
    3 => 'unless you of course include Mondays',
    4 => 'which are also pretty great days too.',
    5 => 'Sometimes Johnny likes picking Strawberrys',
    6 => 'with his mother in the fields',
    7 => 'but sometimes he likes picking blueberries'
];

// preg_quote this because we're looking for the string, not for a pattern it might contain
$findstring = preg_quote("Sundays which are also pretty good");
// htmlentities this in case it contains a string of characters which happen to be an html entity
$replacestring = htmlentities("Mondays which are also pretty great");

// Combine array into one string
// We use htmlentitles to escape the ampersand, so we can use it as a sentence delimeter
$mystring = implode("&", array_map('htmlentities', $myarray));

// Turns $findString into:
// S&?u&?n&?d&?a&?y&?s&? &?w&?h&?i&?c&?h&? &?a&?r&?e&?
// &?a&?l&?s&?o&? &?p&?r&?e&?t&?t&?y&? &?g&?o&?o&?d
$regexstring = implode("&?", str_split($findstring));

// Johnny likes to go to school&but he only likes to go on Saturday&because Saturdays are the
// best days&unless you of course include Mondays&which are also pretty great days
// too.&Sometimes Johnny likes picking Strawberrys&with his mother in the fields&but sometimes
// he likes picking blueberries
$finalstring = preg_replace("/$regexstring/", $replacestring, $mystring);

// Break string back up into array, and return any html entities which might have existed
// at the beginning.
$replacedarray = array_map('html_entity_decode', explode("&", $finalstring));

var_dump($replacedarray);