Agreed, when I read that you didn't have much experience with multi-dimensional arrays, the first thing that came to my mind was "He is pretty new to PHP". I d

Agreed, when I read that you didn't have much experience with multi-dimensional arrays, the first thing that came to my mind was "He is pretty new to PHP". I don't see how you could have built any substantial project in CI/PHP without coming across them. That being said, I think saying I don't know is fine, but be aware of how you say it. If it is a shrugging "I don't know", that would be bad. A positive "I don't know yet", would show you are being honest and willing to educate yourself.