Repeat pattern with foreach within PGFPlots within frame beamer

I'd like to draw multiple dashed lines to visual the slope of a line. I'm not yet familiar with foreach, but I think this should somehow work.

The code below gives the following error:

! Undefined control sequence. \x , \y l.14 \end{axis}

What goes wrong? And how to fix it?

As it seems you want to draw a stair function, maybe you don't need a loop. You could try instead a constant plot, with

Example:





You could use