Re: [Matplotlib-users] Scatter plot with a specific size per point

[Tony Yu <ts...@gm...>]

On Mon, Mar 26, 2012 at 8:26 AM, Matthieu Brucher <
mat...@gm...> wrote:

> Indeed, a little bit less simple, but the solution nonetheless.
>
> Thank you!
>
>
> 2012/3/26 Zachary Pincus <zac...@ya...>
>
>> > I'd like to display a scatter plot where the size for each element is
>> fixed. Currently, when I modify the size of the figure, the size of a
>> marker is fixed, and I would like it to be proportional to the window.
>> > I want this because the size of the marker indicates an extent, and I
>> would like it to confirm that the extents correctly cover the other points.
>>
>> If it's truly an extent, you might be better off drawing polygons of the
>> extent boundaries in the graph's coordinate system -- then things will
>> scale as you desire. This will require digging down a bit into the object
>> API -- make a new matplotlib.collections.PolyCollection (or
>> RegularPolyCollection), and add it to your axes with Axes.add_collection().
>>
>> Zach
>> ---------------------------------------------------------------------
>
>
I needed something similar a while back, and Jae-Joon Lee helped me find a
decent solution. Here're the results for square markers:

#~~~
import matplotlib.collections as collections
import matplotlib.transforms as transforms

class SquareCollection(collections.RegularPolyCollection):
    """Return a collection of squares."""

    def __init__(self, **kwargs):
        super(SquareCollection, self).__init__(4, rotation=np.pi/4.,
**kwargs)

    def get_transform(self):
        """Return transform scaling circle areas to data space."""
        ax = self.axes
        pts2pixels = 72.0 / ax.figure.dpi
        scale_x = pts2pixels * ax.bbox.width / ax.viewLim.width
        scale_y = pts2pixels * ax.bbox.height / ax.viewLim.height
        return transforms.Affine2D().scale(scale_x, scale_y)
#~~~

 Example use<https://github.com/tonysyu/mpltools/blob/master/mpltools/special/hinton.py>
.

Best,
-Tony