Problems setting xticks about nc-time-axis HOT 8 CLOSED

The issue in @MartinDix's initial comment is a symptom of the issue identified in #79 (comment): the ndays attribute -- now the resolution attribute -- cannot be computed without knowing the range of the axis, which is not known at the time the locator is constructed. In the case of setting the ticks it seems that matplotlib creates a new locator and so any axis range information is lost.

This is OK. I propose working around this in nc-time-axis in the following way:

1. Set a default date format in NetCDFTimeDateFormatter if the locator does not have a resolution attribute. I would suggest "%Y-%m-%d" to be consistent with matplotlib. Note that when a user explicitly sets the ticks for a datetime axis, matplotlib also uses a default format.
2. Create another formatter class that will let users set their own date formats to override this default format if they desire. Matplotlib does this with their DateFormatter class (see for example here). I think this would be a useful feature regardless.

To make the analogy with matplotlib clear, I might suggest renaming NetCDFTimeDateFormatter to AutoCFTimeFormatter -- possibly after a deprecation cycle, though I think it is unlikely anyone is using it outside nc-time-axis -- and naming the new formatter proposed in (2) CFTimeFormatter.

Does anyone in @SciTools/nc-time-axis-devs or this issue have any thoughts on this proposal?

from nc-time-axis.

I have a similar problem. A minimal example is that,

import matplotlib.pyplot as plt
import nc_time_axis
import numpy
import cftime

x = [nc_time_axis.CalendarDateTime(cftime.datetime(y, 1, 1), "360_day")
     for y in range(2000, 2010)]
y = numpy.arange(10)
plt.scatter(x, y)
plt.show()

only works if numpy.array is wrapped around the definition of x.

I believe the solution is to put the following here,

        if isinstance(value, np.ndarray) or isinstance(value, list):

from nc-time-axis.

I think I'm having a similar problem here. There is an incompatibility between nc-time-axis and native matplotlib datetime locators. See my issue at proplot-dev/proplot#126.

With a numpy datetime axis:

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import numpy as np
import xarray as xr

times = np.arange('1990', '2000', dtype='datetime64[M]')
data = xr.DataArray(
    np.random.rand(len(times)),
    dims=['time'],
    coords=[times]
)

f, ax = plt.subplots()

ax.plot(data.time, data)
ax.xaxis.set_major_locator(mdates.YearLocator(2))

With a cftime axis:

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import numpy as np
import xarray as xr

times = xr.cftime_range('1990', '2000', freq='M')
data = xr.DataArray(
    np.random.rand(len(times)),
    dims=['time'],
    coords=[times]
)

f, ax = plt.subplots()

ax.plot(data.time, data)
ax.xaxis.set_major_locator(mdates.YearLocator(1))

from nc-time-axis.

@lukelbd, do you think this would be a relatively quick fix? This looks like a somewhat dead repo given how old this issue is. I am very unfamiliar with these locators. Would it just require a few lines of code in __init__? Any thoughts?

from nc-time-axis.

This might be a pretty big PR unfortunately, but shouldn't be very conceptually complicated. You basically need to copy + modify YearLocator, MonthLocator, etc. in matplotlib/dates.py, and that section of code is ~300 lines long. You'd have to go through each line and convert the datetime64 syntax to nc-time-axis syntax -- e.g. wherever they get integer year from a datetime64 array, change that to how you'd get the integer year from a cftime array, etc.

If you have time go for it, but otherwise it might make more sense to convert your nc-time-axis times to datetime64 if possible, even if the calendars don't technically match (my understanding is the main difference between these two formats is that nc-time-axis can work with different calendar types?). Also if you don't get a response to a PR submitted to this repo, I can add your locators directly to proplot just like I add some fixes for currently active cartopy/matplotlib issues.

from nc-time-axis.

Oh, now I see the specific issue at the top is different and possibly easier to fix.

The user was trying to manually set the tick locations by sending a cftime array to set_xticks, which results in matplotlib applying a FixedLocator as the axis locator. However, nc-time-axis evidently expects the axis locator to be its own special locator, and raises an error otherwise (at least this is what I suspect is happening; you should try to print(self.locator) in that example). I don't think there is an issue when using FixedLocator with datetime64 coordinates, so this appears to be an unfortunate limitation of nc-time-axis. Might be simple to fix or might be complicated, depends on how this was designed. But you'll need to play round.

Since this repo has had no commits for >1 year I'd be open to just adding the entire repo's codebase to proplot. Definitely fits within proplot's scope of easier plotting/xarray integration. But that's a long term goal... maybe this summer.

from nc-time-axis.

See #84 for a proof of concept.

from nc-time-axis.

The proposal in #41 (comment) has been implemented in #84. See the PR description for an example of using the new CFTimeFormatter.

from nc-time-axis.