On Wed, Jul 11, 2012 at 11:23 AM, John Hunter <jdh2358@gmail.com> wrote:

On Wed, Jul 11, 2012 at 10:09 AM, Damon McDougall <damon.mcdougall@gmail.com> wrote:
Well, as Ben said, that error fill plot is neato! It doesn't look too
complicated, either. I'd be more than happy to port it over later today
when I get bored of typing up my thesis. It'll probably only take me
about 30 minutes.

If nobody is opposed to this idea, I'll go ahead and submit a PR this
evening (British Summer (hah!) Time).

While it is a nice graph, I am not sure that the use case is common enough to justify a new plotting method.  One can get the same result with:

  In [68]: x = np.linspace(0, 2 * np.pi)

  In [69]: y_sin = np.sin(x)

  In [70]: err = np.concatenate([y_sin + 0.2, y_sin[::-1] - 0.2])

  In [71]: plot(x, y_sin)
  Out[71]: [<matplotlib.lines.Line2D object at 0x96959ec>]

  In [72]: fill_between(np.concatenate([x, x[::-1]]), err, facecolor='red', alpha=0.5)
  Out[72]: <matplotlib.collections.PolyCollection object at 0x962758c>

Admittedly the [::-1] thing is a bit counter-intuitive, but rather than adding a new plotting method, perhaps we would be better off with a helper method to create the xs and ys for fill_between

  xs, ys = mlab.pad_line(x, y, 0.2)
  fill_between(xs, ys)


I could definitely agree with a pad_line() function.  We might want to revisit the issue of how much visibility the mlab module should get in the documentation (it currently doesn't get much at all).  My whole take on mlab was that it was a left-over from the days of working around issues in NumPy and SciPy and that it was being slowly phased out.  As for other possible locations, cbook feels like it is more for the devs than for the users, and adding it to pyplot would render the whole purpose of creating this function as opposed to errorfill moot.

As an additional point about such a pad_line function, it should probably be nice to mirror the errorbar() functionality to allow not only a constant error, but also a N, Nx1, or 2xN array of +/- error. (note that errorbar() for the 2xN array case does -row1 and +row2).

Ben Root