I am trying to break a string of binary ones and zeros into groups of four. After reading the manual and the posts I am missing something:
$subject = "101010101";
$pattern = "/.{1,4}/";
$blocks = preg_split ($pattern, $subject);
print_r($blocks);
The result is an empty array.
Array
(
[0] =>
[1] =>
[2] =>
[3] =>
)
php >
You could just use str_split() which will split your string into an array of strings of size n.
$subject = "101010101";
$split = str_split($subject, 4);
print_r($split);
Output:
Array
(
[0] => 1010
[1] => 1010
[2] => 1
)
You get that result because you are matching 1 - 4 characters to split on. It will match all the characters in the string leaving nothing to display.
If you want to use a regex to break it up into groups of 4 (and the last one because there are 9 characters) you could use preg_match_all and match only 0 or 1 using a character class instead of using a dot which will match any character except a newline.
[01]{1,4}
$subject = "101010101";
$pattern = "/[01]{1,4}/";
$blocks = preg_match_all ($pattern, $subject, $matches);
print_r($matches[0]);
Result
Array
(
[0] => 1010
[1] => 1010
[2] => 1
)
Any char in a string match your pattern, in other words, any string contains only delimiters. And result contains zero-sized spaces.
The get expected result you need capture only delimiters. You can do that adding two flags
$blocks = preg_split ($pattern, $subject, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY );
You can set PREG_SPLIT_DELIM_CAPTURE flag to get captured pattern in output
If this flag is set, parenthesized expression in the delimiter pattern will be captured and returned as well.
PHP reference
Note:- You need to add the pattern into capturing group () to get it in ouput
$subject = "101010101";
$pattern = "/(.{1,4})/";
$blocks = preg_split ($pattern, $subject, null, PREG_SPLIT_DELIM_CAPTURE);
print_r($blocks);
preg_split() returns an array containing substrings of subject split along boundaries matched by pattern, or FALSE on failure.. But you are trying to grab 1-4 characters group from that string. So preg_match_all() can be used for this purpose. Example:
$subject = "101010101";
$pattern = "/[01]{1,4}/";
preg_match_all($pattern, $subject, $match);
echo '<pre>', print_r($match[0]);
preg_split()uses theregexto identify the delimiter. You don't needregexfor this job,str_split()is better because it is faster (and easier to understand).