如何从熊猫的字符串中提取前 8 个字符

Question

我在数据框中有一列，我正在尝试从字符串中提取 8 位数字。我该怎么做

    Input
 Shipment ID
20180504-S-20000
20180514-S-20537
20180514-S-20541
20180514-S-20644
20180514-S-20644
20180516-S-20009
20180516-S-20009
20180516-S-20009
20180516-S-20009

预期产出

Order_Date
20180504
20180514
20180514
20180514
20180514
20180516
20180516
20180516
20180516

我尝试了下面的代码，但没有用。

data['Order_Date'] = data['Shipment ID'][:8]

Answer 1

您很接近，需要索引，str适用于Series 的每个值：

data['Order_Date'] = data['Shipment ID'].str[:8]

如果没有NaNs 值，为了获得更好的性能：

data['Order_Date'] = [x[:8] for x in data['Shipment ID']]

print (data)
        Shipment ID Order_Date
0  20180504-S-20000   20180504
1  20180514-S-20537   20180514
2  20180514-S-20541   20180514
3  20180514-S-20644   20180514
4  20180514-S-20644   20180514
5  20180516-S-20009   20180516
6  20180516-S-20009   20180516
7  20180516-S-20009   20180516
8  20180516-S-20009   20180516

如果str按位置省略代码过滤器列，则前 N 个值如：

print (data['Shipment ID'][:2])
0    20180504-S-20000
1    20180514-S-20537
Name: Shipment ID, dtype: object