Pandas`drop_duplicates`没有保留第一行

Question

我创建了一个具有重复行的Dataframe，如下所示：

df = pd.DataFrame({"Order Date": ["January 1, 2017", "March 15, 2017", "April 20, 2017", "June 23, 2017", "December 12, 2017", None, "April 20, 2017", "April 20, 2017"], 
         "Sales Person": ["John", "John", "Rick", "Mary", "Mary", "Rick", "Rick", "Rick"],
         "Items Sold": [4, -999, 1, np.nan, 7, 3, 1, 1],
         "Item Price": [4.99, 1.99, 9.99, 19.99, 0.99, 2.99, 9.99, 9.99]})

在Jupyter中看起来像这样：

如果我得到重复项，它会正确显示两行重复。

df[df.duplicated()]

然后我调用drop_duplicates删除第二个副本并保留第一个副本。

df.drop_duplicates()

然而，看起来它正在删除两行而不是保留第一行。我错过了drop_duplicates方法中的内容吗？ docstring表示keep参数默认为first，即使我明确地输入了该参数，这仍然会发生。

Answer 1

您的示例中有三个重复的行，使用keep= False查看所有行

df[df.duplicated(keep=False)]
Out[661]: 
   Item Price  Items Sold      Order Date Sales Person
2        9.99         1.0  April 20, 2017         Rick
6        9.99         1.0  April 20, 2017         Rick
7        9.99         1.0  April 20, 2017         Rick

然后，drop_duplicates只保留第1行第3行索引= 2

df.drop_duplicates()
Out[659]: 
   Item Price  Items Sold         Order Date Sales Person
0        4.99         4.0    January 1, 2017         John
1        1.99      -999.0     March 15, 2017         John
2        9.99         1.0     April 20, 2017         Rick
3       19.99         NaN      June 23, 2017         Mary
4        0.99         7.0  December 12, 2017         Mary
5        2.99         3.0               None         Rick