René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[ENH]: API discussion for grouped bar charts","articleBody":"### Problem\r\n\r\nCurrently, if one wants to draw multiple categories of bars side-by-side as in https://matplotlib.org/devdocs/gallery/lines_bars_and_markers/barchart.html, one has to calculate the bar positions manually. This is really a nuissance and too low level for any user-facing interface. Actually, when asked I recommend to use pandas plotting functions for that if possible, which is really embarrasing.\r\n\r\nThere have been stalled attempts to do this (issure 10610, PR #11048). Additionally, this often gets related to a function for stacked bars #14086.\r\n\r\n\r\n\r\n### Proposed solution\r\n\r\nI'd like to pick up this topic and come up with a reasonable API. This topic is really complex and one can easily get lost in various details. For the design procedure, I take a bottom-up appoach by starting with a basic function `grouped_bar()` that does only expose the minimal functionality to get the plot done. I then intended to additional parameters one by one as they fit in. - So don't be concerned that the first proposal here is quite basic.\r\n\r\n**Terminology** I'll use *label* for the x-values, i.e. 'G1' .. 'G5' in above example, and *group* for the categories, i.e. 'Tea'/'Coffee'.\r\n\r\n---\r\n\r\n###  For now: Only vertical orientation\r\nI'll limit the discussion here to 'vertical'. We can have a separate discussion whether we want to add an *orientation* parameter or make a `grouped_barh`. Both are technically easy and only an API design decision that's orthogonal to the rest of the API.\r\n\r\n### For now: Only grouped layout, no stacked layout\r\nTo keep things simple, I'll limit myself to grouped for now, because:\r\n- Stacked is somewhat simpler than grouped as you only need to insert the *bottom* values in multiple calls. For two bars it's just the heights of the firsts, and a cumsum for more than two.\r\n- We may build a separate `stacked_bar()` function, if the first bullet point is considered too cumbersome.\r\n- It's conceivable to unite both in one function as poposed in #11048 and realized in `DataFrame.plot.bar`, but that needs careful additional consideration.\r\n\r\neither way let's defer stacked bars to later.\r\n\r\n### Minimal API\r\n\r\nWe want to be able to rewrite https://matplotlib.org/devdocs/gallery/lines_bars_and_markers/barchart.html as\r\n\r\n```\r\ngrouped_bar(labels, [tea_means, coffee_means], group_labels=['Tea', 'Coffee']) \r\n```\r\n\r\nThus, the minimal API is:\r\n\r\n```\r\ndef grouped_bar(x, heights, *, group_labels=None):\r\n    \"\"\"\r\n    Parameters\r\n    -----------\r\n    x : array-like of str\r\n         The labels.\r\n    heights : list of array-like:\r\n         An iterable of array-like: The iteration runs over the groups.\r\n         Each individual array-like is the list of label values for that group.\r\n    group_labels : array-like of str, optional\r\n         The labels of the data groups.\r\n    \"\"\"\r\n```\r\n\r\n---\r\n\r\nI'll soon expand on the minimal API, answering a lot of questions from https://github.com/matplotlib/matplotlib/pull/11048#issuecomment-381812675. But before that, please speak up in case you have fundamental concerns with adding such functionality at all or with the bottom-up design approach. OTOH if you think this is worth pursuing, please give a :+1:.","author":{"url":"https://github.com/timhoffm","@type":"Person","name":"timhoffm"},"datePublished":"2022-10-30T22:21:28.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":27},"url":"https://github.com/24313/matplotlib/issues/24313"}