Display labels in the same order as grids when plotting in vertical mode

[alexcb]

This PR changes the order of the legend to match the order of the plotted grids when plotting with vertical=True

Before this PR:

After this PR:

Signed-off-by: Alex Couture-Beil alex@mofo.ca

[gyli]

Thanks for the PR!! I might need to test it with more parameters as it's more related to starting_location. Similar thing happens when starting_location='SE' or 'NE', that blocks are plotted from right to left, while the order of legend is not changed. Thinking if we need a new parameter for flipping the legend.

[alexcb]

The parameter might do the trick.

I noticed a different issue where if I use a sum of values that are less than 100, I get an empty box in the top right corner, when I would expect it to be in the bottom right instead.

[gyli]

That is because the default value of starting_location is 'SW', so it starts plotting from bottom left to top right, since it's using coordinate system within matplotlib. So you will have to set starting_location='NW'.

[alexcb]

Setting starting_location='NW' did the trick -- thanks!

data = [50, 40, 9.4]
labels = ['fifty', 'fourty', 'nine point four']
fig = plt.figure(
    figsize=(10.0, 3.0),
    dpi=100,
    FigureClass=pywaffle.Waffle,
    starting_location='NW',
    vertical=True,
    rows=10,
    columns=10,
    values=data,
    labels=labels,
    legend={'loc': 'upper left', 'bbox_to_anchor': (1, 1)},
)
fig.savefig('test.png', bbox_inches='tight')

produces

It does seem a bit strange that one needs to specify both vertical=True and starting_location='NW' to get a plot like this with the legend correctly ordered. One possibility could be to set starting_location='auto' which would pick NW when vertical, and maintain the existing default otherwise. Then in the case of the starting location being South, then perhaps the legend order should be reversed?

[gyli]

I am trying to compare these two solutions:

1. Your solution, adding starting_location='auto'. Not as default value for now, but could be default in future version. When vertical=True, it's just starting_location='NW' Pros: match the legend of course, especially without flipping the legend. Otherwise the order of values and legend would be different too. Cons: auto is not clear enough to explain how the starting_location is chosen

2. Adding parameter flip_legend, allowing us to flip it manually when needed. Pros: Consistent plotting direction; User is notified when legend and values follow different order, as they need to manually specify this parameter Cons: Flipped legend order might be unexpected as it's different to value order

Any idea or any pros/cons you would like to add?

[alexcb]

After playing around a bit more with different data points, I would agree with 2, seems like it offers the most flexibility for various users' cases without trying to guess what the user wants to do.