[英]Numpy 3d array indexing
I have a 3d numpy array ( n_samples x num_components x 2 ) in the example below n_samples = 5 and num_components = 7. 我在下面N_SAMPLES次 = 5和num_components = 7的示例的三维numpy的阵列(N_SAMPLES次X num_components×2)。
I have another array ( indices ) which is the selected component for each sample which is of shape ( n_samples ,). 我有另一个数组( 索引 ),它是每个样本的选定组件( n_samples ,)。
I want to select from the data array given the indices so that the resulting array is n_samples x 2 . 我想从给定索引的数据数组中进行选择,以便得到的数组是n_samples x 2 。
The code is below: 代码如下:
import numpy as np
np.random.seed(77)
data=np.random.randint(low=0, high=10, size=(5, 7, 2))
indices = np.array([0, 1, 6, 4, 5])
#how can I select indices from the data array?
For example for data 0, the selected component should be the 0th and for data 1 the selected component should be 1. 例如,对于数据0,所选组件应为第0,对于数据1,所选组件应为1。
Note that I can't use any for loops because I'm using it in Theano and the solution should be solely based on numpy. 请注意,我不能使用任何for循环,因为我在Theano中使用它,解决方案应该完全基于numpy。
To get component #0, use 要获得组件#0,请使用
data[:, 0]
ie we get every entry on axis 0 (samples), and only entry #0 on axis 1 (components), and implicitly everything on the remaining axes. 即我们得到轴0(样本)上的每个条目,只有轴1(组件)上的条目#0,以及其余轴上的所有条目。
This can be easily generalized to 这可以很容易地推广到
data[:, indices]
to select all relevant components. 选择所有相关组件。
But what OP really wants is just the diagonal of this array, ie (data[0, indices[0]], (data[1, indices[1]]), ...)
The diagonal of a high-dimensional array can be extracted using the diagonal
function: 但OP真正想要的只是这个数组的对角线,即
(data[0, indices[0]], (data[1, indices[1]]), ...)
高维数组的对角线可以使用对diagonal
函数提取:
>>> np.diagonal(data[:, indices])
array([[7, 7, 4, 8, 5],
[4, 3, 5, 2, 8]])
(You may need to transpose the result.) (您可能需要转置结果。)
Is this what you are looking for? 这是你想要的?
In [36]: data[np.arange(data.shape[0]),indices,:]
Out[36]:
array([[7, 4],
[7, 3],
[4, 5],
[8, 2],
[5, 8]])
You have a variety of ways to do so, but this is my loop recommendation: 您有多种方法可以这样做,但这是我的循环建议:
selection = np.array([ datum[indices[k]] for k,datum in enumerate(data)])
The resulting array, selection
, has the desired shape. 得到的阵列
selection
具有所需的形状。
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