関連ワード:  dataframe change data type of column    pandas change data type of column    pandas change data type of column to string    pandas change data type of column to datetime    pandas change data type of column to categorical    pandas change data type of column from object to string    pandas change data type of column to int    pandas change data type of column from object to int    pandas change data type of column from object to float    pandas change data type of column to float