如何从熊猫中的字符串中提取前8个字符
Posted
技术标签:
【中文标题】如何从熊猫中的字符串中提取前8个字符【英文标题】：How to extract first 8 characters from a string in pandas 【发布时间】：2019-01-07 11:55:48 【问题描述】：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。我该怎么做呢
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
我尝试了下面的代码，它没有工作。
data['Order_Date'] = data['Shipment ID'][:8]
【问题讨论】：
【参考方案1】：你也可以决定从-S删除到最后
df["Order_Date"]=df['Shipment ID'].replace(regex=r"\-.*",value="")
df
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
您还可以捕获前 8 位数字，然后删除所有内容并用捕获组的反向引用替换：
df['Shipment ID'].replace(regex=r"(\d8).*",value="\\1")
【讨论】：
【参考方案2】：你也可以使用str.extract
例如：
import pandas as pd
df = pd.DataFrame('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'])
df["Order_Date"] = df["Shipment ID"].str.extract(r"(\d8)")
print(df)
输出：
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
【讨论】：
【参考方案3】：您很接近，需要使用str 进行索引，这适用于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
如果省略str代码按位置过滤列，前N个值如：
print (data['Shipment ID'][:2])
0 20180504-S-20000
1 20180514-S-20537
Name: Shipment ID, dtype: object
【讨论】：
以上是关于如何从熊猫中的字符串中提取前8个字符的主要内容，如果未能解决你的问题，请参考以下文章