How to check for double occurence of a string and delete one

[Joseph Cobham]

Hello...
I woulk like to know if ther is any php pre designed function that checks a string and searches through it to there is one or more occurence of a phrase or another string and deletes all the other ones and leave only one occurency of the string or phrase

[Dormilich]

there isn’t a single function but a combination of 2 functions and a little bit of logic should solve that.