Q:

Formula for a vertical cosine graph

I was looking at Cosine and I thought it was cool, I was wondering what the formula for a horizontal version of it would look like.
A graph for Something like this :

A:

To flip a function along the line $y=x$ then just switch $x$ and $y$.  The graph of the picture above is a function of $y$:
$$x = f(y) = \cos y.$$

