Re: [Matplotlib-users] How to place an image colorbar next to the image when there are several subplots ?

[Fabrice S. <si...@lm...>]

Le jeudi 19 février 2015 à 23:10 -0800, Peter Rowat a écrit :
> I apologize for asking such a trivial question, but I’ve spent a long time trying to fix this:
> 
> I have a large 2D array that displays as an image, with a colorbar on the side.
> I also display 2 curves on top of the image. i.e. in same axes.
> The following code does it:
> 
>     fig,ax = plt.subplots()
>     cax = ax.imshow(bighistT, extent=myextent, cmap = cm.coolwarm, aspect = myaspect,\
>         interpolation='nearest')
>     ax.set_title("Dummy title")
>     # Add colorbar
>     cbar = fig.colorbar(cax)
>     ax.set_ylabel('mV')
> 
>     ax.plot(emtrate, emrate, '.r')                  #curve 1
>     ax.plot(tt, rate*50 - 25.0, '-k', linewidth=3)  #curve 2
> 
>     plt.show()
> ========
> IN FACT,
> I want the curves in separate axes, below the image while the colorbar remains immediately to the right
> of the image.
> 
> I've tried many minor variations, for way over an hour..
> I've looked at demos, read about colorbar in several different parts of matplotlib docs...
> 
> Can someone help?? .... Either the colorbar is next to the last plot, or else I
> get an error.
> 
> Here is code that I've tried: It puts the colorbar in the wrong place, and in addition the image size
> is very small while the ax2 and ax3 curve plots are much wider. 
> I want the image and the second 2 plots the same width.
> 
> 
>     fig, (ax1, ax2,ax3) = plt.subplots(3,1)
>     cax = ax1.imshow(bighistT, extent=myextent, cmap = cm.coolwarm, aspect = myaspect,\
>         interpolation='nearest')
>     ax1.set_title("Dummy title")
>     # Add colorbar
> #   cbar = fig.colorbar(cax)  # this places the colorbar next to the third subplot
>     plt.colorbar(cax)         # so does this

cax is not the Axes containing the image, but the image itself. It seems
that you want to "steal" some space to the first subplot so:

        fig, (ax1, ax2,ax3) = plt.subplots(3,1)
        im = ax1.imshow(bighistT, extent=myextent, cmap=cm.coolwarm,
        		aspect=myaspect, interpolation='nearest')
        ax1.set_title("Dummy title")
        cbar = fig.colorbar(im, ax=ax1)

or you can also create a new Axes between ax1 and ax2, and tell
colorbar() to put the Colorbar into (with the cax keyword argument)

See
http://matplotlib.org/api/figure_api.html#matplotlib.figure.Figure.colorbar

-- 
Fabrice