python - 从 pandas 数据框中识别相似数据集中的第一行

Question

我有一个类似于下图的数据框:

    BillNumber Description            LineAmount   TotalAmount
0   INV001     Line Item 1 of INV001  500          700
1   INV001     Line Item 2 of INV001  200          700
2   INV002     Line Item 1 of INV002  100          800
3   INV002     Line Item 2 of INV002  300          800
4   INV002     Line Item 3 of INV002  400          800

我想要的是这样的:

    BillNumber Description            LineAmount   TotalAmount  NewBill
0   INV001     Line Item 1 of INV001  500          700          Yes
1   INV001     Line Item 2 of INV001  200          700
2   INV002     Line Item 1 of INV002  100          800          Yes
3   INV002     Line Item 2 of INV002  300          800
4   INV002     Line Item 3 of INV002  400          800

我想识别每个新 BillNumber 的第一行，并在名为“NewBill”的新列下为它标记值“Yes”。我们如何使用 pandas 实现这一目标？

提前致谢。

Answer 1

使用numpy.where与 Series.duplicated :

df['NewBill'] = np.where(df['BillNumber'].duplicated(), '', 'Yes')
print (df)
  BillNumber            Description  LineAmount  TotalAmount NewBill
0     INV001  Line Item 1 of INV001         500          700     Yes
1     INV001  Line Item 2 of INV001         200          700        
2     INV002  Line Item 1 of INV002         100          800     Yes
3     INV002  Line Item 2 of INV002         300          800        
4     INV002  Line Item 3 of INV002         400          800