条件preg_replace

Question

I've the following code:

$formula = "E1 + E2 + E4 + E5 + E7 + E8 + E10 + E11";

$patterns = array('Se' => '@Se@',
                  'Et' => '@Et@',
                  'E1' => '@E1@',
                  'E2' => '@E2@');

$values = array('Se' => 9,
                'Et' => 12,
                'E1' => 1,
                'E2' => 8);

$replaced = preg_replace($patterns, $values, $formula);

echo $replaced; 
"1 + 8 + E4 + E5 + E7 + E8 + 10 + 11"

I need a code that only replace E1, and ignore E10 and E11, in this case showing the following result: "1 + 8 + E4 + E5 + E7 + E8 + E10 + E11"

thanks!

Answer 1

<?php
$formula = "E1 + E2 + E4 + E5 + E7 + E8 + E10 + E11";

$patterns = array('@\bSe\b@',
                  '@\bEt\b@',
                  '@\bE1\b@',
                  '@\bE2\b@');

$values = array(9, 12, 1, 8);

$replaced = preg_replace($patterns, $values, $formula);

echo $replaced; 

Outputs:

1 + 8 + E4 + E5 + E7 + E8 + E10 + E11

Edit. Your code refactored for better reading:

<?php
$formula = "E1 + E2 + E4 + E5 + E7 + E8 + E10 + E11";

$map = array(
    'Se' => 9,
    'Et' => 12,
    'E1' => 1,
    'E2' => 8,
);

$patterns = array_keys($map);
$patterns = array_map(function ($v) { return "/\b$v\b/"; }, $patterns);

$values = array_values($map);

$replaced = preg_replace($patterns, $values, $formula);

echo $replaced;

Run it