熊猫警告SettingWithCopyWarning：试图在DataFrame的切片副本上设置一个值

Question

我似乎无法理解为什么我从下面的熊猫代码中得到警告： 我正在尝试使用下面的代码将titanic.csv数据集中的“性别”列转换为数字：

from sklearn import preprocessing
label_encoding = preprocessing.LabelEncoder()
titanic_df['Sex'] =label_encoding.fit_transform(titanic_df['Sex'].astype(str))
titanic_df.head()

我收到此警告：

<ipython-input-41-45071618b7c1>:4: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
  titanic_df['Sex'] =label_encoding.fit_transform(titanic_df['Sex'].astype(str))

如何格式化代码以避免出错？