如何将日期数组传递给pcolor图？

Question

我有矩阵数据，其中一个轴与日期有关。但是，我在将此数据作为轴传递给pcolor时遇到问题。我的虚拟数据如下：

In [219]: X = [datetime.date.today() + datetime.timedelta(days=i) for i in range(4)]

In [220]: Y = arange(5)

In [221]: Z = arange(4*5).reshape(4, 5)

天真的尝试pcolor(Y, X, Z)失败，因为pcolor不想获得list个对象：

In [222]: pcolor(Y, X, Z)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-222-1ece18b4bc13> in <module>()
----> 1 pcolor(Y, X, Z)

/export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/pyplot.py in pcolor(*args, **kwargs)
   2926         ax.hold(hold)
   2927     try:
-> 2928         ret = ax.pcolor(*args, **kwargs)
   2929         draw_if_interactive()
   2930     finally:

/export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/axes.py in pcolor(self, *args, **kwargs)
   7545         shading = kwargs.pop('shading', 'flat')
   7546 
-> 7547         X, Y, C = self._pcolorargs('pcolor', *args, allmatch=False)
   7548         Ny, Nx = X.shape
   7549 

/export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/axes.py in _pcolorargs(funcname, *args, **kw)
   7357 
   7358         Nx = X.shape[-1]
-> 7359         Ny = Y.shape[0]
   7360         if len(X.shape) != 2 or X.shape[0] == 1:
   7361             x = X.reshape(1, Nx)

AttributeError: 'list' object has no attribute 'shape'

将其转换为包含array的{​​{1}}失败并显示datetime.date：

TypeError: float() argument must be a string or a number, not 'datetime.date'

最后，将其转换为正确的In [223]: pcolor(Y, numpy.array(X), Z) --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-223-a00423a6d479> in <module>() ----> 1 pcolor(Y, numpy.array(X), Z) /export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/pyplot.py in pcolor(*args, **kwargs) 2926 ax.hold(hold) 2927 try: -> 2928 ret = ax.pcolor(*args, **kwargs) 2929 draw_if_interactive() 2930 finally: /export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/axes.py in pcolor(self, *args, **kwargs) 7606 kwargs['antialiaseds'] = False 7607 -> 7608 collection = mcoll.PolyCollection(verts, **kwargs) 7609 7610 collection.set_alpha(alpha) /export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/collections.py in __init__(self, verts, sizes, closed, **kwargs) 743 Collection.__init__(self, **kwargs) 744 self._sizes = sizes --> 745 self.set_verts(verts, closed) 746 747 def set_verts(self, verts, closed=True): /export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/collections.py in set_verts(self, verts, closed) 763 codes[0] = mpath.Path.MOVETO 764 codes[-1] = mpath.Path.CLOSEPOLY --> 765 self._paths.append(mpath.Path(xy, codes)) 766 else: 767 self._paths.append(mpath.Path(xy)) /export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/path.py in __init__(self, vertices, codes, _interpolation_steps, closed, readonly) 131 vertices = vertices.astype(np.float_).filled(np.nan) 132 else: --> 133 vertices = np.asarray(vertices, np.float_) 134 135 if codes is not None: /export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/numpy/core/numeric.py in asarray(a, dtype, order) 460 461 """ --> 462 return array(a, dtype, copy=False, order=order) 463 464 def asanyarray(a, dtype=None, order=None): TypeError: float() argument must be a string or a number, not 'datetime.date' 对象也无法解决问题，导致numpy.datetime64失败：

Invalid type promotion

在这里进行的正确方法是什么？在

请注意，the question plotting date data with pcolor的答案使用的是In [224]: pcolor(Y, numpy.array(X, dtype="datetime64[D]"), Z) --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-224-0ac06cfafa35> in <module>() ----> 1 pcolor(Y, numpy.array(X, dtype="datetime64[D]"), Z) /export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/pyplot.py in pcolor(*args, **kwargs) 2926 ax.hold(hold) 2927 try: -> 2928 ret = ax.pcolor(*args, **kwargs) 2929 draw_if_interactive() 2930 finally: /export/data/home/gholl/venv/gerrit/lib/python3.4/site-packages/matplotlib/axes.py in pcolor(self, *args, **kwargs) 7577 X4[:, newaxis], Y4[:, newaxis], 7578 X1[:, newaxis], Y1[:, newaxis]), -> 7579 axis=1) 7580 verts = xy.reshape((npoly, 5, 2)) 7581 TypeError: invalid type promotion ，而不是scatter，因此对我的情况没有帮助。

Answer 1

Matplotlib使用简单的浮点数来表示日期时间。因此，您必须先转换它们，然后告诉轴必须将标签格式化为日期。 Matplotlib为此提供函数date2num：

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import datetime
import numpy as np

# Your original data (with adapted sizes)
x = [datetime.date.today() + datetime.timedelta(days=i) for i in range(4)]
y = np.arange(5)
z = np.arange(3*4).reshape(3, 4).T

# Convert to numbers
x = mdates.date2num(x)

# Create the figure
fig, ax = plt.subplots(1,1)
plt.pcolor(x,y,z)

# Setup the DateFormatter for the x axis
date_format = mdates.DateFormatter('%D')
ax.xaxis.set_major_formatter(date_format)

# Rotates the labels to fit
fig.autofmt_xdate()

plt.show()

其他一些评论：

• 对于pcolor，x和y向量表示图块的角点。因此，它们需要比数据长1个元素。
• documentation提供了如何在matplotlib中处理日期的精彩概述。

结果：