如何从 pandas 字符串中提取前8个字符 [英] How to extract first 8 characters from a string in pandas

问题描述

我在数据框中有一个列，我正在尝试从字符串中提取8位数字.我该怎么办

I have column in a dataframe and i am trying to extract 8 digits from a string. How can I do it

    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

预期产量

Order_Date
20180504
20180514
20180514
20180514
20180514
20180516
20180516
20180516
20180516

我尝试了下面的代码，但没有用.

I tried below code and it didnt work.

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

推荐答案

您很接近，需要使用str进行索引，该索引适用于Serie s的每个值:

You are close, need indexing with str which is apply for each value of Series:

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

如果没有NaN的值，则为获得更好的性能:

For better performance if no NaNs values:

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:

If omit str code filter column by position, first N values like:

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

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