How to extract first 8 characters from a string in pandas

Question

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

Expected Output

Order_Date
20180504
20180514
20180514
20180514
20180514
20180516
20180516
20180516
20180516

I tried below code and it didnt work.

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

Answer 1

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

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

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

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

Answer 2

You can also use str.extract

Ex:

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)

Output:

       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