• numpy.piecewise中的多个部分（如何在numpy中实现多字段排序）
• "import numpy as np" ImportError: No module named numpy
• 3.7Python 数据处理篇之 Numpy 系列 (七)---Numpy 的统计函数
• Anaconda Numpy 错误“Importing the Numpy C Extension Failed”是否有另一种解决方案
• Difference between import numpy and import numpy as np

numpy.piecewise中的多个部分（如何在numpy中实现多字段排序）

我正在上模糊系统课程，并在计算机上记笔记。这意味着我不得不不时在计算机上绘制图形。由于这些图的定义非常明确，因此我认为将其绘制numpy为一个好主意（我使用LaTeX做笔记，并且在python
shell上相当快，因此我认为可以摆脱这种情况）。

模糊隶属函数的图形是高度分段的，例如：

为了对此进行绘图，我尝试使用以下代码进行编码numpy.piecewise（这给了我一个神秘的错误）：

In [295]: a = np.arange(0,5,1)In [296]: condlist = [[b<=a<b+0.25, b+0.25<=a<b+0.75, b+0.75<=a<b+1] for b in range(3)]---------------------------------------------------------------------------ValueError                                Traceback (most recent call last)<ipython-input-296-a951e2682357> in <module>()----> 1 condlist = [[b<=a<b+0.25, b+0.25<=a<b+0.75, b+0.75<=a<b+1] for b in range(3)]ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()In [297]: funclist = list(itertools.chain([lambda x:-4*x+1, lambda x: 0, lambda x:4*x+1]*3))In [298]: np.piecewise(a, condlist, funclist)---------------------------------------------------------------------------ValueError                                Traceback (most recent call last)<ipython-input-298-41168765ae55> in <module>()----> 1 np.piecewise(a, condlist, funclist)/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/numpy/lib/function_base.pyc in piecewise(x, condlist, funclist, *args, **kw)    688     if (n != n2):    689         raise ValueError(--> 690                 "function list and condition list must be the same")    691     zerod = False    692     # This is a hack to work around problems with NumPy''sValueError: function list and condition list must be the same

在这一点上，我对如何绘制此函数感到很困惑。我不太了解错误消息，这进一步阻碍了我调试该错误的努力。

最终，我希望将这个函数绘制并导出到EPS文件中，因此，我也很感谢这些帮助。

答案1

通常，当您仅将代码编写为数字时，numpy数组非常擅长做明智的事情。链接比较是罕见的例外之一。您看到的错误本质上是这样的（piecewise内部和ipython错误格式对此进行了混淆）：

>>> a = np.array([1, 2, 3])>>> 1.5 < aarray([False,  True,  True], dtype=bool)>>> >>> 1.5 < a < 2.5Traceback (most recent call last):  File "<stdin>", line 1, in <module>ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()>>> >>> (1.5 < a) & (a < 2.5)array([False,  True, False], dtype=bool)>>>

您也可以使用np.logical_and，但是按位and工作就可以了。

就绘图而言，numpy本身不执行任何操作。这是matplotlib的示例：

>>> import numpy as np>>> def piecew(x):...   conds = [x < 0, (x > 0) & (x < 1), (x > 1) & (x < 2), x > 2]...   funcs = [lambda x: x+1, lambda x: 1, ...            lambda x: -x + 2., lambda x: (x-2)**2]...   return np.piecewise(x, conds, funcs)>>>>>> import matplotlib.pyplot as plt>>> xx = np.linspace(-0.5, 3.1, 100)>>> plt.plot(xx, piecew(xx))>>> plt.show() # or plt.savefig(''foo.eps'')

注意这piecewise是一个反复无常的野兽。特别是，它需要将其x参数设置为数组，如果不是，则甚至不会尝试对其进行转换（numpy用语：x需要为ndarray，而不是array_like）：

>>> piecew(2.1)Traceback (most recent call last):  File "<stdin>", line 1, in <module>  File "<stdin>", line 4, in piecew  File "/home/br/.local/lib/python2.7/site-packages/numpy/lib/function_base.py", line 690, in piecewise    "function list and condition list must be the same")ValueError: function list and condition list must be the same>>> >>> piecew(np.asarray([2.1]))array([ 0.01])

"import numpy as np" ImportError: No module named numpy

问题：没有安装 numpy

解决方法：

下载文件，安装

numpy-1.8.2-win32-superpack-python2.7

安装运行 import numpy，出现

Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    import numpy
  File "C:\Python27\lib\site-packages\numpy\__init__.py", line 153, in <module>
    from . import add_newdocs
  File "C:\Python27\lib\site-packages\numpy\add_newdocs.py", line 13, in <module>
    from numpy.lib import add_newdoc
  File "C:\Python27\lib\site-packages\numpy\lib\__init__.py", line 8, in <module>
    from .type_check import *
  File "C:\Python27\lib\site-packages\numpy\lib\type_check.py", line 11, in <module>
    import numpy.core.numeric as _nx
  File "C:\Python27\lib\site-packages\numpy\core\__init__.py", line 6, in <module>
    from . import multiarray
ImportError: DLL load failed: %1 不是有效的 Win32 应用程序。

原因是：python 装的是 64 位的，numpy 装的是 32 位的

重新安装 numpy 为：numpy-1.8.0-win64-py2.7

3.7Python 数据处理篇之 Numpy 系列 (七)---Numpy 的统计函数

目录

[TOC]

前言

具体我们来学 Numpy 的统计函数

（一）函数一览表

调用方式：np.*

（二）统计函数 1

（1）说明

（2）输出

.sum(a)

.mean(a)

.average(a)

.std(a)

.var(a)

（三）统计函数 2

（1）说明

（2）输出

.max(a) .min(a)

.ptp(a)

.median(a)

.argmin(a)

.argmax(a)

.unravel_index(index,shape)

作者：Mark

日期：2019/02/11 周一

Anaconda Numpy 错误“Importing the Numpy C Extension Failed”是否有另一种解决方案

  \Traceback (most recent call last):
File "C:\Conda\envs\gcp\lib\site-packages\numpy\core\__init__.py",line 22,in <module>
from . import multiarray
File "C:\Conda\envs\gcp\lib\site-packages\numpy\core\multiarray.py",line 12,in <module>
from . import overrides
File "C:\Conda\envs\gcp\lib\site-packages\numpy\core\overrides.py",line 7,in <module>
from numpy.core._multiarray_umath import (
ImportError: DLL load Failed while importing _multiarray_umath: The specified module Could not be found.

During handling of the above exception,another exception occurred:

Traceback (most recent call last):
File "c:\API\citi-bike.py",line 4,in <module>
import numpy as np
File "C:\Conda\envs\gcp\lib\site-packages\numpy\__init__.py",line 150,in <module>
from . import core
File "C:\Conda\envs\gcp\lib\site-packages\numpy\core\__init__.py",line 48,in <module>
raise ImportError(msg)
ImportError:

IMPORTANT: PLEASE READ THIS FOR ADVICE ON HOW TO SOLVE THIS ISSUE!

Importing the numpy C-extensions Failed. This error can happen for
many reasons,often due to issues with your setup or how NumPy was
installed.

We have compiled some common reasons and troubleshooting tips at:

https://numpy.org/devdocs/user/troubleshooting-importerror.html

Please note and check the following:

* The Python version is: python3.9 from "C:\Conda\envs\gcp\python.exe"
* The NumPy version is: "1.21.1"

and make sure that they are the versions you expect.
Please carefully study the documentation linked above for further help.

Original error was: DLL load Failed while importing _multiarray_umath: The specified module Could not be found.

import numpy as np

import numpy.f2py as myf2py

import numpy as np
np.f2py #throws no module named f2py

import numpy as np # np is an alias pointing to numpy, but at this point numpy is not linked to numpy.f2py
import numpy.f2py as myf2py # this command makes numpy link to numpy.f2py. myf2py is another alias pointing to numpy.f2py as well

import numpy

import numpy as np

import numpy
np = numpy
del numpy

import numpy as np
import numpy.f2py   # OK
import np.f2py      # ImportError

import scipy.ndimage.interpolation as warp
warp.affine_transform(I, ...)

try:
    import pyfftw.interfaces.numpy_fft as fft
except:
    import numpy.fft as fft
# call fft.ifft(If) with fftw or the numpy fallback under a common name

import numpy as np
np.f2py