如何在 Pandas 中为字符串添加前导零格式？
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How to add leading zero formatting to string in Pandas?
提问by Student
Objective:To format ['Birth Month']with leading zeros
目标：['Birth Month']用前导零格式化
Currently, I have this code:
目前，我有这个代码：
import pandas as pd
import numpy as np
df1=pd.DataFrame.from_items([('A', [1, 2, 3]), ('B', [4, 5, 6])])
df1['Birth Year']= np.random.randint(1905,1995, len(df1))
df1['Birth Month']= str(np.random.randint(1,12, len(df1))).zfill(2)
df1
Which produces a list of values in ['Birth Month']which is not what I need:
这产生了一个值列表，['Birth Month']其中不是我需要的：
A B Birth Year Birth Month
0 1 4 1912 [4 5 9]
1 2 5 1989 [4 5 9]
2 3 6 1921 [4 5 9]
Instead, I am looking for values and formatting like the following in ['Birth Month']:
相反，我正在寻找如下所示的值和格式['Birth Month']：
A B Birth Year Birth Month
0 1 4 1912 04
1 2 5 1989 12
2 3 6 1921 09
回答by EdChum
Cast the dtype of the series to strusing astypeand use vectorised str.zfillto pad with 0:
将系列的 dtype 投射到strusingastype并使用矢量化str.zfill来填充0：
In [212]:
df1=pd.DataFrame.from_items([('A', [1, 2, 3]), ('B', [4, 5, 6])])
df1['Birth Year']= np.random.randint(1905,1995, len(df1))
df1['Birth Month']= pd.Series(np.random.randint(1,12, len(df1))).astype(str).str.zfill(2)
df1
Out[212]:
A B Birth Year Birth Month
0 1 4 1940 09
1 2 5 1945 04
2 3 6 1962 03
All you did was assign a scalar value (which is why every row is the same) and convert the element to a str of a list:
您所做的只是分配一个标量值（这就是为什么每一行都相同的原因）并将元素转换为列表的 str ：
In [217]:
df1['Birth Month'].iloc[0]
Out[217]:
'[3 6 9]'
You can see the result of the assignment here broken down:
您可以在此处查看分配的结果细分：
In [213]:
(np.random.randint(1,12, len(df1)))
Out[213]:
array([5, 7, 4])
In [214]:
str(np.random.randint(1,12, len(df1))).zfill(2)
Out[214]:
'[2 9 5]'
