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nan:not a number
inf:infinity;正无穷
numpy中的nan和inf都是float类型
t!=t 返回bool类型的数组(矩阵)
np.count_nonzero() 返回的是数组中的非0元素个数;true的个数。
np.isnan() 返回bool类型的数组。
那么问题来了,在一组数据中单纯的把nan替换为0,合适么?会带来什么样的影响?
比如,全部替换为0后,替换之前的平均值如果大于0,替换之后的均值肯定会变小,所以更一般的方式是把缺失的数值替换为均值(中值)或者是直接删除有缺失值的一行
demo.py(numpy,将数组中的nan替换成对应的均值):
# coding=utf-8 import numpy as np def fill_ndarray(t1): for i in
range(t1.shape[1]): # 遍历每一列(每一列中的nan替换成该列的均值) temp_col = t1[:, i] # 当前的一列
nan_num = np.count_nonzero(temp_col != temp_col) if nan_num != 0: #
不为0,说明当前这一列中有nan temp_not_nan_col = temp_col[temp_col == temp_col] #
去掉nan的ndarray # 选中当前为nan的位置,把值赋值为不为nan的均值 temp_col[np.isnan(temp_col)] =
temp_not_nan_col.mean() # mean()表示求均值。 return t1 if __name__ == '__main__': t1
= np.array([[ 0., 1., 2., 3., 4., 5.], [ 6., 7., np.nan, np.nan, np.nan,
np.nan], [12., 13., 14., 15., 16., 17.], [18., 19., 20., 21., 22., 23.]]) t1 =
fill_ndarray(t1) # 将nan替换成对应的均值 print(t1) ''' [[ 0. 1. 2. 3. 4. 5.] [ 6. 7. 12.
13. 14. 15.] [12. 13. 14. 15. 16. 17.] [18. 19. 20. 21. 22. 23.]] '''