python - 一些列在缩放后变成了 NaN

Question

我正在尝试使用这样的功能来扩展功能

def featureNormalize(X):
'''
This function takes the features as input and
returns the normalized values, the mean, as well 
as the standard deviation for each feature.
'''
X_norm = (X - np.mean(X))/np.std(X)
mu = np.mean(X)
sigma = np.std(X)
return X_norm, mu, sigma

然后调用它

X, mean, std = featureNormalize(X) ## We call the function over the features

动车组	测试集

所以它适用于我的火车组。

但是当我将其称为测试集时]，某些列完全变成了 Nan 两个集合都没有 Nan 或 null 值。我试图用nanmeanand重写这个函数nanstd，但是没有用：

def featureNormalize(X):
    X_norm = (X - np.nanmean(X, dtype = 'float32')) / np.nanstd(X, dtype = 'float32')
    mu = np.nanmean(X, dtype = 'float32')
    sigma = np.nanstd(X, dtype = 'float32')
    return X_norm, mu, sigma

什么会导致这个问题，我该怎么办