NumPy 数组中元素的索引 [英] Index of element in NumPy array

问题描述

在 Python 中，我们可以使用 .index() 来获取数组中某个值的索引.

但是对于 NumPy 数组，当我尝试这样做时:

decoding.index(i)

我明白了:

<块引用>

AttributeError: 'numpy.ndarray' 对象没有属性 'index'

如何在 NumPy 数组上执行此操作?

解决方案

使用 np.where 获取给定条件为 True 的索引.

示例:

对于名为 a 的二维 np.ndarray:

i, j = np.where(a == value) # 比较整数数组时i, j = np.where(np.isclose(a, value)) # 比较浮点数组时

对于一维数组:

i, = np.where(a == value) # 整数i, = np.where(np.isclose(a, value)) # 浮点数

请注意，这也适用于 >=、<=、!= 等条件...

您还可以使用 index() 方法创建 np.ndarray 的子类:

class myarray(np.ndarray):def __new__(cls, *args, **kwargs):返回 np.array(*args, **kwargs).view(myarray)定义索引(自我，价值):返回 np.where(self == value)

测试:

a = myarray([1,2,3,4,4,4,5,6,4,4,4])a.index(4)#(数组([ 3, 4, 5, 8, 9, 10]),)

In Python we can get the index of a value in an array by using .index().

But with a NumPy array, when I try to do:

decoding.index(i)

I get:

AttributeError: 'numpy.ndarray' object has no attribute 'index'

How could I do this on a NumPy array?

解决方案

Use np.where to get the indices where a given condition is True.

Examples:

For a 2D np.ndarray called a:

i, j = np.where(a == value) # when comparing arrays of integers

i, j = np.where(np.isclose(a, value)) # when comparing floating-point arrays

For a 1D array:

i, = np.where(a == value) # integers

i, = np.where(np.isclose(a, value)) # floating-point

Note that this also works for conditions like >=, <=, != and so forth...

You can also create a subclass of np.ndarray with an index() method:

class myarray(np.ndarray):
    def __new__(cls, *args, **kwargs):
        return np.array(*args, **kwargs).view(myarray)
    def index(self, value):
        return np.where(self == value)

Testing:

a = myarray([1,2,3,4,4,4,5,6,4,4,4])
a.index(4)
#(array([ 3,  4,  5,  8,  9, 10]),)

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