NumPy数组中的元素索引

In Python we can get the index of a value in an array by using .index(). How can I do it with a NumPy array?

在Python中，我们可以使用.index（）获取数组中值的索引。我怎么能用NumPy数组做到这一点？

When I try to do

当我尝试做的时候

decoding.index(i)

it says that the NumPy library doesn't support this function. Is there a way to do it?

它说NumPy库不支持这个功能。有办法吗？

3 个解决方案

#1

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

使用np.where获取给定条件为True的索引。

Examples:

例子：

For a 2D np.ndarray:

对于2D np.ndarray：

i, j = np.where(a == value)

For a 1D array:

对于1D阵列：

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

Which works for conditions like >=, <=, != and so forth...

适用于> =，<=，！=等条件......

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

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

Testing:

测试：

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

#2

You can convert a numpy array to list and get its index .

您可以将numpy数组转换为list并获取其索引。

for example

例如

tmp = [1,2,3,4,5] #python list
a = numpy.array(tmp) #numpy array
i = list(a).index(2) # i will return index of 2, which is 1

i is just what you want.

我就是你想要的。

#3

I'm torn between these two ways of implementing an index of a NumPy array:

我在实现NumPy数组索引的这两种方式之间徘徊：

idx = list(classes).index(var)
idx = np.where(classes == var)

Both take the same number of characters, but the second method returns an int, instead of a nparray.

两者都使用相同数量的字符，但第二种方法返回int，而不是nparray。

#1