Re: [matplotlib-devel] Stacked plotting in matplotlib

[Damon M. <dam...@gm...>]

Hey Nic,

Thanks for bringing this up. I was the author for #819, so I'd like to
get some dicussion going on this, too. Sorry for the delay, I was in the
midst of writing a thesis, which I am now free of.

On Sun, Aug 12, 2012 at 11:51:24PM -0500, Nic Eggert wrote:
> Hi all,
> 
> I'd like to bring up a question spurred by PRs #847(mine) and #819
> (recently accepted). These PRs both deal with stacked plots. #819 adds the
> stackplot function to axes.py as a new function, which plots different 2-d
> datasets stacked atop each other. #847 slightly modifies the functioning of
> `hist` in axes.py by adding a new kwarg which allows datasets to be
> stacked. Currently this is only possible using the `barstacked` histtype.
> #847 makes it also work with the `step` and `stepfilled` histtypes.
> 
> One of the issues that has been raised in the comments of #847 is whether
> we want to take this opportunity to come up with a unified way to handle
> "stacked-ness". Michael Droettboom suggested I raise this issue on this
> list. So far, there are 3 different approaches:
> 
> 1. The state before #819. AFAIK the only way to do any sort of stacking was
> to call `hist` with `histtype="barstacked"`. This treats stacked histograms
> as a different type of histogram than non-stacked histograms. One of my
> motivations for writing #847 was to get stacked step and stepfilled
> histograms, which would require adding several new histtypes (stepstacked
> and stepfilledstacked). It seems to me that histtype mostly controls the
> style of the histogram plotted, and shouldn't have anything to do with
> "stacked-ness", so I think this is kind of clunky.
> 
> 2. The approach I take in #847. Add a new kwarg which controls whether or
> not multiple datasets are stacked. I think this is the cleanest
> implementation, although that's probably obvious because it's how I wrote
> my PR. To keep everything consistent in this approach, we should remove the
> stackplot function added in #819, and move that functionality to the `plot`
> function, adding a `stacked` kwarg there.
> 
> 3. The approach of #819. With this approach, we would add a separate
> function to handle stacked versions of different plots. I'd re-write #847
> as a new function called `stackhist`. This approach, IMO, doesn't scale
> well if we want to add "stacked-ness" to more plot types in the future.

I'm in favour of numero dos, even though for #819 I took approach number
3. I didn't really think about the bigger picture here with regards to
stackedness of other plot types. But since seeing your stacked histogram
changeset, this seems like a more sensible route.

I say this with zero authority, though.

It'd be nice to have a few people chime in with their two cents.

> Please take a look at this and send comments about these proposals or any
> others you might have. I hope the community can come to a consensus which
> unifies the handling of stacked-ness.
> 
> Whatever we end up choosing, I think adding a stacked step histogram will
> make it much easier to promote the use of mpl in high energy physics, where
> we use this style of plot frequently.
> 
> Thanks,
> 
> Nic Eggert
> Graduate Fellow
> Cornell University


-- 
Damon McDougall
http://www.damon-is-a-geek.com
B2.39
Mathematics Institute
University of Warwick
Coventry
West Midlands
CV4 7AL
United Kingdom