if-statement: PHP- How to check whether a variable consists of a number and a letter (eg: 3a)

vendredi 6 octobre 2017

I have to read a ecxel file and I identify the rows I need based on the row number. Unfortunatly the rows are like this:

So what I do is, I check each row with a for-loop and then I have if-statement where only the topics with 1a,1b,2a, ... , 29c should pass.

for($i=19 ; $i<173 ; $i++){
            "code"
            if( ??? )){
                "code";
            }
        }

Do you have any idea how to realize that?

Thank you?

if-statement