python-3.x - 如何从 Pandas 字符串中提取前8个字符

Question

我在数据框中有列，我正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

预期输出

Order_Date
20180504
20180514
20180514
20180514
20180514
20180516
20180516
20180516
20180516

我尝试下面的代码，它没有工作。

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

Answer 1

您接近了，需要使用str进行索引，该索引适用于Serie的每个值:

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

如果没有 NaN的值，则为获得更好的性能:

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

如果按位置省略 str代码过滤器列，则前N个值如下:

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