非零值的整数平均值 [英] Numpy mean of nonzero values
问题描述
我有一个大小为N * M的矩阵,我想找到每一行的平均值.值是从1到5,并且没有任何值的条目设置为0.但是,当我想使用以下方法查找均值时,它给了我错误的均值,因为它还计算了具有值的条目0.
I have a matrix of size N*M and I want to find the mean value for each row. The values are from 1 to 5 and entries that do not have any value are set to 0. However, when I want to find the mean using the following method, it gives me the wrong mean as it also counts the entries that have value of 0.
matrix_row_mean= matrix.mean(axis=1)
如何获取非零值的均值?
How can I get the mean of only nonzero values?
推荐答案
获取每一行中非零的计数,并将其用于平均每一行的总和.因此,实现看起来像这样-
Get the count of non-zeros in each row and use that for averaging the summation along each row. Thus, the implementation would look something like this -
np.true_divide(matrix.sum(1),(matrix!=0).sum(1))
如果您使用的是较旧版本的NumPy,则可以使用计数的浮点转换来替换np.true_divide
,就像这样-
If you are on an older version of NumPy, you can use float conversion of the count to replace np.true_divide
, like so -
matrix.sum(1)/(matrix!=0).sum(1).astype(float)
样品运行-
In [160]: matrix
Out[160]:
array([[0, 0, 1, 0, 2],
[1, 0, 0, 2, 0],
[0, 1, 1, 0, 0],
[0, 2, 2, 2, 2]])
In [161]: np.true_divide(matrix.sum(1),(matrix!=0).sum(1))
Out[161]: array([ 1.5, 1.5, 1. , 2. ])
解决问题的另一种方法是用NaNs
替换零,然后使用np.nanmean
,这将忽略那些NaNs
而实际上是那些原始的zeros
,就像-
Another way to solve the problem would be to replace zeros with NaNs
and then use np.nanmean
, which would ignore those NaNs
and in effect those original zeros
, like so -
np.nanmean(np.where(matrix!=0,matrix,np.nan),1)
从性能的角度来看,我建议使用第一种方法.
From performance point of view, I would recommend the first approach.
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