Report date and time of cursor position on a plot_date plot

When plotting with DateTime on the x axis, it would be useful to show both the date and time in the cursor position. Currently only the date or time is shown, depending on zoom level.

Example: only the date is shown in bottom left (x=2016-10-16)

Current master installed using pip, Linux, python 3.5.2

@anntzer

The value shown the bar is by default pulled from the axis Formaterr via the format_data_short method. The default implementation is just the delegate to fomat_data which in turn delegates to __call__ (for historical reasons).

To trace through the call path here, in backend_bases.NavigationToolbar2.mouse_move (which is hooked up to the mouse move callback) calls Axes.format_coord and puts the result in the GUI msg area. format_coord (in axes/_base.py) calls format_xdata / format_ydata which in turn check if there is a user supplied fmt_xdata or fmt_ydata attributes on the Axes object and if not calls the axis's major formatters format_data_short method.

The specific work here is:

add a format_data_short method to the auto data formatter that uses the next more precise format from what __call__ uses.

attn @anntzer

I don't think there's a way to make this work for everyone, in the sense that most of the time I'd think you'd only want to use the date OR the time? Probably a doc recipe (which could be, in an ideal world, as simple as ax.xaxis.get_major_formatter().format_data_short = lambda pos: lambda pos: mdates.num2date(pos).strftime("%Y-%m-%d; %H:%M:%S") would be better?

Anyways, while trying to come up with such a recipe, I found a bunch of issues with datetime and ticker handling.

matplotlib.dates should probably export its own strftime function which transparently handles matplotlib timestamps (avoiding the need to call num2date explicitly).
The fact that formatters are callable, which I argued against in New Formatter API #5804, makes it possible to write ax.format_xdata = Formatter(...) (e.g. examples/api/date_demo.py), which is a mess as the axes' formatter instance is not correctly set, so format_data_short confusingly doesn't work -- that example really needs to be changed to something like

import time
_fmt = mdates.DateFormatter('%Y-%m-%d')
_fmt.format_data_short = lambda pos: mdates.num2date(pos).strftime("%Y-%m-%d; %H:%M:%S")
ax.xaxis.set_major_formatter(_fmt)

or alternatively we should just make Axes.format_xdata a property that redirects to Axes.xaxis.major.formatter, so that one can assign to format_xdata and then to format_xdata.format_data_short. (Actually the second solution isn't bad...)
In other words the pile of redirections going on is really hard to keep track of. (Unlabeling as "easy" and "new-contributor-friendly" for this reason.)

examples/api/date_index_formatter.py makes no sense, especially its docstring? Neither plot is labelling or plotting week-ends.

The two use cases I currently frequently encounter are:

Looking at a large scale overview (as above), but wanting to know the time of an obvious feature
Zooming into data (e.g. the data above) to look at precisely where a feature is, but then loosing information about the date. This means having to zoom back out again to try and find the feature in 'date zoomlevel'.

Even if you want to know one or the other, showing both doesn't (as far as I can see) impact on this.

My point was that showing too much info could be slightly annoying when the timescale is obviously either very large or very small, but I guess that's not a big cost (and erring on the side of too much info is probably better). In that case I'd suggest always showing cursor data either with the %c (locale) strftime format, or with isoformat().

#10084 does the annoying thing of the big label. Its actually not that annoying.

Perhaps this feature needs a complete overhaul? Perhaps supporting a format string with named components? That way, the user can easily customize the output. The hard part will be trying to automatically generate a good default format string.

…

On Sat, Mar 24, 2018 at 12:42 AM, Jody Klymak ***@***.***> wrote: #10084 <#10084> does the annoying thing of the big label. Its actually not that annoying. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#7582 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AARy-NnE_qQ_8mmGiPek4TnozYqWfTUCks5thc6lgaJpZM4LGnli> .

there is a method to change that display, but I forget what its called.

Ax.format_cursor

I think this has improved enough for me to close the original issue now.

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Report date and time of cursor position on a plot_date plot #7582

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Report date and time of cursor position on a plot_date plot #7582

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tacaswell commented on Dec 7, 2016

anntzer commented on Dec 7, 2016

dstansby commented on Dec 7, 2016

anntzer commented on Dec 7, 2016

jklymak commented on Mar 24, 2018

WeatherGod commented on Mar 24, 2018

jklymak commented on Mar 24, 2018

jklymak commented on Mar 24, 2018

dstansby commented on Apr 8, 2018

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