Plot of various density numbers verses galaxy colour

[Keith Sloan]

I wish to make a number of plots of density function values versus galaxy colour.

Okay I can select a subset of galaxies based on u - r or just r.

But how do I calc the density function for individual galaxies?

The use of bins reduces the number of values, do I make the bin size 1 and how do I do that? I assume with numpy.

Are the calculations valid with a bin size of one?