[Matplotlib-users] Plotting incomplete data sets

I have some data, which I'd like to plot using matplotlib. Some of the data
has been flagged by some other software, and I have a boolean array, the
same shape as my original data which tells me which data has been flagged.
What I'd like to do is plot the unflagged data as a single pixels ',' and
flagged data as crosses 'x'.

At the moment I'm plotting all of the data as single pixels, and then
replotting everything as crosses, setting the unflagged data to some
negative number and setting the axes to hide them away off the bottom of the
graph, however this approach is a bit of a pain as you often end up with the
crosses showing up on the bottom of the graph etc.

I'm sure I can get this approach to work but I thought I'd ask if there's
there a more elegant way to achieve the same aim.

Many thanks in advance,

John Morgan