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Added test_pcolor in test_datetime.py #27391

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Added test_pcolor in test_datetime.py #27391

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3d353e9
added test case for pcolor
rawwash Nov 29, 2023
fd4c2c5
adding datetime to pcolor
rawwash Nov 29, 2023
7316aaa
pcolor with correct datetime functionality
rawwash Nov 30, 2023
9a0ac90
removing if main
rawwash Nov 30, 2023
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15 changes: 12 additions & 3 deletions lib/matplotlib/tests/test_datetime.py
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Expand Up @@ -399,11 +399,20 @@ def test_matshow(self):
fig, ax = plt.subplots()
ax.matshow(...)

@pytest.mark.xfail(reason="Test for pcolor not written yet")
@mpl.style.context("default")
def test_pcolor(self):
fig, ax = plt.subplots()
ax.pcolor(...)
base_date = datetime.date(2020, 1, 1)
dates = [base_date + datetime.timedelta(days=i) for i in range(10)]
data = np.random.rand(10, 10)
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If you want to use randomness, you will need to set a seed (we use 19680801 for tests) or else the test image will change on each run.

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Sounds good, will add this seed to ensure the image does not change in each run.

data = np.sort(data, axis=0)
fig, ax = plt.subplots()
c = ax.pcolor(data, cmap='viridis')
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There is no use of dates in this call.

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Both axes of pcolor require that I pass numerical data, how do you suggest I use dates? I can use datetime in this call, but then I would have to use date2num, which defies the purpose. Not sure how else to implement. This is what I found online:

'In my understanding, you would like to have date formatted tick labels for axes when using 'pcolor'. You cannot directly provide 'pcolor' with datetime vectors as of now.
However, there is a way to use the ' datenum ' and ' datetick ' functions to get datetime axes tick labels as illustrated in the example below:
%Creating two example vectors of datetimes, tx and ty
t1 = datetime(2017,9,2,0,0,0);
t2 = datetime(2017,9,30,0,0,0);
tx = t1:5:t2;
ty = tx + day(15);
%Creating an example C matrix for pcolor plot
C = magic(length(tx));
% Using datenum to convert to real numbers for plotting and dateticks for
% date labelling. You can play around with datetick options to suit your needs
pcolor(datenum(tx), datenum(ty), C);
datetick('y', 'dd-mm-yy', 'keepticks');
datetick('x', 'dd-mm-yy', 'keepticks');'

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X and Y in fact, CAN take date info directly, no need to call date2num...

>>> tx = ty = np.arange('2005-02', '2005-03', dtype='datetime64[D]')
>>> tx, ty = np.meshgrid(tx, ty)
>>> c = np.arange(tx.size).reshape(tx.shape)
>>> plt.pcolor(tx, ty, c)

yields
test

While I made no effort to clean up the labels so they were visible/not overlapping, the point stands that they are properly converted as desired/as is the point of these tests.

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The answer you found is Matlab code about Matlab's plotting, which matplotlib was originally inspired by, but has diverged from significantly since then.

ax.set_title('Pseudocolor Plot with Datetime Data')
ax.set_xticks(range(len(dates)))
ax.set_xticklabels([d.strftime('%Y-%m-%d') for d in dates], rotation=45)
fig.colorbar(c, ax=ax)
fig.tight_layout()
plt.close(fig)

@pytest.mark.xfail(reason="Test for pcolorfast not written yet")
@mpl.style.context("default")
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