Re: [Matplotlib-users] Best way to plot a 2d histogram?

[Ernest A. <ead...@gm...>]

Hi,

 1/10/09 @ 18:17 (-0700), thus spake Matthew Neeley:
> Here is a snippet that might get you started:
> 
> 
> import numpy as np
> from matplotlib import pyplot as plt
> from matplotlib import cm
> import mpl_toolkits.mplot3d as plt3
> 
> data = np.random.random((8,8))**4
> cmap = cm.RdBu
> 
> fig = plt.figure()
> ax = plt3.Axes3D(fig)
> 
> d = 0.1
> 
> w, h = data.shape
> for x in range(w):
>     for y in range(h):
>         ax.bar3d([x+d], [y+d], [0], 1-d, 1-d, data[x,y], cmap(data[x,y]))
> ax.set_zlim3d((0, 1))
> plt.show()
> 
> Obviously, you should replace data with the actual data you want to
> plot (maybe numpy can help with the histogramming), and use an
> appropriate cmap for your data.  Note that in this case the entire box
> is a single color, not shaded up the side as in the example you
> referenced; I actually like it this way but I also don't know how one
> would do the shading in matplotlib.  I'll admit it's rather silly to
> have to create all these boxes individually, but that's the only way I
> could see to color each box according to its height.  The variable d
> just puts gaps between boxes; you could set this to zero to make the
> boxes adjacent.
> 
> I haven't figured out how to properly set the tick labels on the x and
> y axis in a 3d plot like this.  Also, there are often some z-order
> errors with boxes occluding each other when they shouldn't.  I don't
> know the details of how these things work internally; maybe some
> experts could weigh in here.

Great!! I like the shading this way, so no problem here.
Too bad about the rendering glitches though. Although, maybe that
can be sorted out by increasing the distance between boxes...? I will
experiment a little with this method of yours as it does basically what
I wanted. If everything fails I think I will finally use a 2-d plot
using a colour map to represent the height of bars,
as in here: http://www.davidbdean.com/wp-content/uploads/hist2d.png

Thanks a lot!

Bye.

-- 
Ernest