Re: [Matplotlib-users] possible bug with linestyle='steps'

[John H. <jd...@gm...>]

On Fri, Jul 17, 2009 at 5:15 PM, Paul Ray<Pau...@nr...> wrote:
>
>
> Ryan Krauss-2 wrote:
>>
>> RTFM:
>>
>> plot(t,y, drawstyle='steps-post')
>>
>>
>
> Actually, 'steps-pre' (which is the default) and 'steps-post' seem to have
> swapped definitions.
> Here is what the docs say:
>    *where*: [ 'pre' | 'post' | 'mid'  ]
>      If 'pre', the interval from x[i] to x[i+1] has level y[i]
>      If 'post', that interval has level y[i+1]
>      If 'mid', the jumps in *y* occur half-way between the
>      *x*-values.
>
> In fact both the default behavior and what you get with steps-pre are what
> SHOULD happen with steps-post.  And steps-post (as you point out) does what
> should be the default behavior and that of steps-pre.
>
> I have filed a bug report on this, since it is very important that this work
> as expected.  As the original poster pointed out, this used to work
> correctly but recently seems to have gotten broken.



I am looking first at the behavior of plot with the drawstyle property
set -- let's make sure this is correct before turning to the steps
command, which just uses plot with the drawstyle set -- here is my
test code

import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure()
ax = fig.add_subplot(111)

a = np.array([1,2,3,4,5])

styles = 'default' , 'steps' , 'steps-pre' , 'steps-mid' , 'steps-post'
styles = 'steps' , 'steps-pre'
for ls in styles:
    ax.plot(a, ls=ls, label=ls, lw=2)

ax.legend(loc='upper left')

plt.show()


pre causes the step to rise on the x[i], post causes it to rise on
x[i+1] and mid in the middle.  This seems like the correct behavior.
So it does look like the docstring for  'step' is incorrect, and I've
changed it to read


        *where*: [ 'pre' | 'post' | 'mid'  ]
          If 'pre', the interval from x[i] to x[i+1] has level y[i+1]

          If 'post', that interval has level y[i]

          If 'mid', the jumps in *y* occur half-way between the


JDH