numpy矩阵,通过对每一行进行排序将0设置为值 [英] numpy matrix, setting 0 to values by sorting each row
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问题描述
我有一个矩阵,有很多行和8列. 每个像元代表当前行属于8个类别中的1个类别的概率. 我想在每行中仅保留2个最大值,并将其余的设置为0.
I have a matrix, with many rows, and 8 columns. Each cell represents a probability for the current row to belong to 1 of the 8 classes. I would like to keep only the 2 highest values in each row, and set the rest to 0.
到目前为止,我唯一想到的方法是分别对每一行进行循环和排序. 例如:
So far, the only way I can think of is by looping and sorting each row separately. For example:
a = np.array([[ 0.2 , 0.1 , 0.02 , 0.01 , 0.031, 0.11 ],
[ 0.5 , 0.1 , 0.02 , 0.01 , 0.031, 0.11 ],
[ 0.2 , 0.1 , 0.22 , 0.15 , 0.031, 0.11 ]])
我想得到:
array([[ 0.2 , 0. , 0. , 0. , 0. , 0.11],
[ 0.5 , 0. , 0. , 0. , 0. , 0.11],
[ 0.2 , 0. , 0.22, 0. , 0. , 0. ]])
谢谢
推荐答案
Here's one vectorized approach with np.argpartition
-
m,n = a.shape
a[np.arange(m)[:,None],np.argpartition(a,n-2,axis=1)[:,:-2]] = 0
样品运行-
In [570]: a
Out[570]:
array([[ 0.94791114, 0.48438182, 0.54574317, 0.45481231, 0.94013836],
[ 0.03861196, 0.99047316, 0.7897759 , 0.38863967, 0.93659426],
[ 0.49436676, 0.93762758, 0.33694977, 0.45701655, 0.73078113],
[ 0.21240062, 0.85141765, 0.00815352, 0.52517721, 0.49752736]])
In [571]: m,n = a.shape
...: a[np.arange(m)[:,None],np.argpartition(a,n-2,axis=1)[:,:-2]] = 0
...:
In [572]: a
Out[572]:
array([[ 0.94791114, 0. , 0. , 0. , 0.94013836],
[ 0. , 0.99047316, 0. , 0. , 0.93659426],
[ 0. , 0.93762758, 0. , 0. , 0.73078113],
[ 0. , 0.85141765, 0. , 0.52517721, 0. ]])
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