Numpy-将列附加到空数组意味着现有数组

Question

我正试图使用numpy模块(作为np导入(来查找列向量的平均值，然后从列中减去平均值。然而，当我试图获取均值并将其附加到一个空数组时，它以0开头，并且具有错误的值。你知道我做错了什么吗？

rating2 = np.array(student_data.values[:,1:])
print(rating2)
means = np.empty([1,25])
for index in range(0,24):
b = np.mean(rating2[:,index], axis = 0)
print("b is", b)
np.append(means,b)
A = np.array(means)
print(A)

我检查了正在计算的每个平均值，但它不是以0开头的。我检查了我的索引，它似乎是正确的。

我的输出：

[[3 2 3 3 3 3 3 3 4 3 4 4 3 4 3 2 2 3 4 2 2 3 3 4 4]
[2 3 4 3 2 3 4 3 3 4 5 3 4 3 3 1 1 3 3 2 1 3 3 4 3]
[2 5 4 2 3 2 4 4 1 4 3 1 4 2 2 3 3 2 2 4 3 2 1 3 2]
[3 4 3 3 3 3 3 3 3 3 3 2 3 3 3 3 3 3 3 4 4 3 3 3 3]
[4 1 1 5 4 4 2 2 4 1 1 4 1 4 4 4 4 4 4 2 4 4 5 2 4]
[4 2 2 4 3 3 2 3 4 2 2 4 2 4 4 3 3 4 4 2 3 4 4 3 4]
[2 5 5 1 2 2 4 4 2 5 5 2 5 2 2 2 2 2 2 4 2 2 1 4 2]
[3 4 3 3 3 3 3 3 2 3 3 2 3 2 3 4 4 3 2 4 4 3 2 2 2]
[4 1 2 4 3 4 2 2 4 2 3 5 3 4 4 3 3 4 4 2 2 4 4 4 4]
[3 4 3 3 3 3 3 3 2 3 2 2 3 2 3 4 4 3 2 4 4 3 3 2 2]]
b is 3.0
b is 3.1
b is 3.0
b is 3.1
b is 2.9
b is 3.0
b is 3.0
b is 3.0
b is 2.9
b is 3.0
b is 3.1
b is 2.9
b is 3.1
b is 3.0
b is 3.1
b is 2.9
b is 2.9
b is 3.1
b is 3.0
b is 3.0
b is 2.9
b is 3.1
b is 2.9
b is 3.1
[[0.  3.  3.1 3.  3.1 2.9 3.  3.  3.  2.9 3.  3.1 2.9 3.1 3.  3.1 2.9 2.9
3.1 3.  3.  2.9 3.1 2.9 3.1]]

Answer 1

这应该能在中工作

import numpy as np
# your numpy array
matrix = np.random.random((10, 10))
# this is the column wise mean
mean = np.mean(matrix, axis=0)
# this line is broadcasting the mean to the matrix
matrix_without_mean = matrix - mean