查找具有多個條件的numpy數組中的元素

Question

如何找到滿足多個條件的Numpy數組中的元素索引？

例如：功能numpy.nonzero讓我根據一些標準查找指數：

In [1]: from numpy import * 
In [2]: a = array([1,0,1,-1]) 
In [5]: nonzero(a != 0) 
Out[5]: (array([0, 2, 3]),) 

但是，讓這樣的多重標準不起作用：

In [6]: nonzero((a != 0) and (a < 0)) 
--------------------------------------------------------------------------- 
ValueError        Traceback (most recent call last) 
/Users/cls/<ipython-input-6-85fafffc5d1c> in <module>() 
----> 1 nonzero((a != 0) and (a < 0)) 

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all() 

在MATLAB中，有可能寫：

find((d != 0) & (d < 0)) 

我怎樣才能做到這一點與NumPy的？

Answer 1

IIUC，您可以使用&代替and：

>>> from numpy import * 
>>> a = array([1,0,1,-1]) 
>>> nonzero(a!=0) 
(array([0, 2, 3]),) 
>>> nonzero((a != 0) and (a < 0)) 
Traceback (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() 
>>> nonzero((a != 0) & (a < 0)) 
(array([3]),) 
>>> where((a != 0) & (a < 0)) 
(array([3]),)