fill step plots

Community matplotlib-users
1

Hi; I've got a rather simple question. I want to (color) fill a step plot below the line, but using the fill() function always creates regular plots, not step plots, and fillstyle doesn't work as I'd expect it to. How can I fill a step plot? Something like this:

import matplotlib.pyplot as plt
x = [0.0,0.5,0.66,0.75,1.0]
y = [0.72,0.72,0.61,0.43,0.33]
plt.step(x, y, fillstyle="bottom") # doesn't work how I imagine...
plt.axis([0.0,1.0,0.0,1.0])
plt.show()

What I want is that the area below the step-plot line is color-filled, but I seem to be unable to find a function for it. If I use plt.fill(), it creates a polygon plot and it does not allow to use the kwarg drawstyle="steps", so I get no further with this function either.

I guess it's a simple problem, but I'm having a bit of a hard time wading though all the API, being completely new to matplotlib, so some help would be very welcome!
--Florian

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2

Florian Leitner wrote:

Hi; I've got a rather simple question. I want to (color) fill a step plot below the line, but using the fill() function always creates regular plots, not step plots, and fillstyle doesn't work as I'd expect it to. How can I fill a step plot? Something like this:

import matplotlib.pyplot as plt
x = [0.0,0.5,0.66,0.75,1.0]
y = [0.72,0.72,0.61,0.43,0.33]
plt.step(x, y, fillstyle="bottom") # doesn't work how I imagine...
plt.axis([0.0,1.0,0.0,1.0])
plt.show()

What I want is that the area below the step-plot line is color-filled, but I seem to be unable to find a function for it. If I use plt.fill(), it creates a polygon plot and it does not allow to use the kwarg drawstyle="steps", so I get no further with this function either.

I guess it's a simple problem, but I'm having a bit of a hard time wading though all the API, being completely new to matplotlib, so some help would be very welcome!
--Florian

It looks to me like there is no easy way to do it. This is a deficiency in the way steps are implemented at present. The generation of the stepped path is buried in a Line2D helper method, and the path is not saved. If it were, its x and y coordinates could be passed to fill_between, which would then provide the effect you want.

Unless and until some refactoring is done in mpl, you will have to manually generate the x and y coordinates corresponding to your stepped line instead of using plt.step.

It may be too much of a change to make to the API now, but I think that the step-generation should not be done in Line2D at all; it should be at the next level up. The Line2D object should not be modifying the coordinates it is given. At the very least, its get_path() should return the actual path it is drawing; at present it does not. This latter change may be relatively easy.

Eric

···

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