Remove comma from string in php

You can explode the string by comma first and then implode after filtering the empty strings.

$val=",2,,4,5,6";
$parts=explode(",",$val);
$parts=array_filter($parts);
echo(implode(",",$parts));

Note that this will also filter 0 from your values. If you want to keep the zeros, refer this question

You can do what you did on your first problem...

Then use trim() to remove unnecessary commas at the front or end of the string.

$mystring = ',2,,4,5,6';

$output = str_replace(',,', ',', $mystring);

echo trim($output, ',');

//Output will be: 2,4,5,6

// Variable Declaration for String
$str = "1,2,,4,5,6";

// Create Array Out of the String, The comma ',' is the delimiter
// This would output 
//       [ 1 => 1, 2 => 2, 3 => '', 4 => 4, 5 => 5, 6 => 6 ]
$explodedStr = explode(',', $str);

// Filter Array And Remove The empty element which in this case
//    3 => ''
$filteredArray = array_filter( $explodedStr );

// Convert Array into String with comma delimiter 
$formattedString = implode(',',  $filteredArray);

1. Trim all commas from the front and back of the string because they are not useful delimiters.
2. Match one or more commas that occur immediately after a comma.

In my pattern, I match a comma, then forget it with \K, then match one or more commas. These extra commas are then replaced with an empty string.

Code: (Demo)

$string = ',1,2,,4,5,,,,6,,,,';
echo preg_replace('/,\K,+/', '', trim($string, ','));
// 1,2,4,5,6