I just installed matplotlib 0.99.0 and I see that this problem is
The command plot(a,ls='steps') is equivalent to plot(a,ls='steps-pre')
and both cause the first value of the array to NOT be plotted. This
is REALLY not what should happen when one plots an array with several
values. It is fine if there is a custom option to make that behavior
(like 'steps-pre'), but the default for ls='steps' or step(x,y) must
be to have the first flat level at the level of the first entry (what
the 'steps-post' does).
The docstring now correctly describes the behavior, so that is good,
but please please make the default "steps" be "steps-post".
On Jul 19, 2009, at 9:35 AM, John Hunter wrote:
> On Fri, Jul 17, 2009 at 5:15 PM, Paul Ray<Paul.Ray@...>
>> Ryan Krauss-2 wrote:
>>> 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
>> 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-
> styles = 'steps' , 'steps-pre'
> for ls in styles:
> ax.plot(a, ls=ls, label=ls, lw=2)
> ax.legend(loc='upper left')
> 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