由操作员拆分数学公式但保留操作员

Question

I'm looking to split the following strings based upon the operator between them. If there is parenthesis then we have to keep the entire parenthesis together.

Here's the types of strings I will have.

(1.25*1.5)-(10.5/2.15625)
(1.25*1.5)+10.75
1.25*(10.5/10.75)
1.25/10.5

The desired output I'm looking for is this

array(){
    [0]=>
    string = "(1.25*1.5)"
    [1]=>
    string = "-"
    [2]=>
    string = "(10.5/2.15625)"
}

array(){
    [0]=>
    string = "(1.25*1.5)"
    [1]=>
    string = "+"
    [2]=>
    string = "10.75"
}

array(){
    [0]=>
    string = "1.25"
    [1]=>
    string = "*"
    [2]=>
    string = "(10.5/10.75)"
}

array(){
    [0]=>
    string = "1.25"
    [1]=>
    string = "/"
    [2]=>
    string = "10.5"
}

this is what I have so far.

$expression_parts = preg_split('~([<>=]+)~', $expression, NULL, 
PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY ) ;

Answer 1

I'll show you a new trick (*SKIP)(*FAIL) this time. This technique is used to match and disqualify targeted substrings.

Code: (Demo)

$strings=[
    '(1.25*1.5)-(10.5/2.15625)',
    '(1.25*1.5)+10.75',
    '1.25*(10.5/10.75)',
    '1.25/10.5'
];
foreach($strings as $string){
//                                                  vvvvvvvv-capture and retain non-numeric characters (delimiters)
    var_export(preg_split('~\([^)]*\)(*SKIP)(*FAIL)|([^\d.])~',$string,NULL,PREG_SPLIT_DELIM_CAPTURE));
//                          ^^^^^^^^^-match and disqualify parentheticals
    echo "
";
}

Output:

array (
  0 => '(1.25*1.5)',
  1 => '-',
  2 => '(10.5/2.15625)',
)
array (
  0 => '(1.25*1.5)',
  1 => '+',
  2 => '10.75',
)
array (
  0 => '1.25',
  1 => '*',
  2 => '(10.5/10.75)',
)
array (
  0 => '1.25',
  1 => '/',
  2 => '10.5',
)

This will also perform very well on your input strings:

preg_match_all('~\([^)]+\)|\d+(?:\.\d+)?|.~',$string,$out)?$out[0]:[]

~                #pattern delimiter
\([^)]+\)        #match parenthetical expression (does not account for nested parentheticals)
|                #or
\d+(?:\.\d+)?    #match integers or floats (notice the ? makes the trailing portion optional
|                #or
.                #match one non-newline character that isn't caught by an earlier "alternative"
~                #pattern delimiter