如何从熊猫中的字符串中提取前8个字符答案

【问题标题】：How to extract first 8 characters from a string in pandas如何从熊猫中的字符串中提取前8个字符
【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

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】：

标签： python-3.x pandas substring

【解决方案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"(\d{8}).*",value="\\1")

【讨论】：

【解决方案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"(\d{8})")
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】：

【解决方案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】：