Question

I have a field in my table that holds a string denoting some object levels, like so:

"<3<"
"<3<5<"
"<3<5<49<"

etc.

I have a function that is to remove a level from such a string, without knowing the position of the level in the string itself. Concretely, I would like to remove “3”. The result should be:

"0"
"<5<"
"<5<49<"

If I would, however, want to remove 5, and not 3, the result should be this:

"<3<"
"<3<"
"<3<49<"

Lastly, if I chose to remove 49 instead of 3 or 5, I would like to get this:

"<3<"
"<3<5<"
"<3<5<"

As you can see, the position of the substring that is to be removed varies – sometimes it’s the leftmost one, sometimes in the middle, sometimes the rightmost one. What is important after all this is:

1. If the number I am removing is the only value, enclosed in “less than” signs (as in “<3<” while removing 3), the new result must be 0.
2. If the number I am removing is not the only value, the only thing that matters is that the final notation stays the same – as in, the entire string must remain enclosed in “less than” symbols, and substrings of multiple “less than” symbols in a row must not happen (as in, “3<<5<” is not allowed).

Is there an easy regex way to handle this with php and mysql, or should I just make 3 manual checks?

P.S. While I may have posed it as such, this is not homework but an actual work issue.

Answer 1

for each line two replacements: (for example, you want to remove “3”)

replace "^<3<$" -> "0"; 
replace "<3" -> "";