Question on how to add strings using Python if conditional statements-CodePudding

I have a question.
I'd appreciate it if you could help me.
I want to add a specific character in the middle of a string using a python ‘if’ statement.
For example,
When I change January 1, 2021 to a string, I want to convert 2020011 (7 letters) to 20200101 (8 letters).
This is my code I have tried

df2['date']=df2['date'].astype(str)
x = df2['date'].str.len()
def date_changing(x) :
    if x == 7: return df2.date.astype(str).apply(lambda z: z[:6]   '0'   z[6:])
    else: return df2.date.astype(str)

df2['new_date']=df2['date'].apply(date_changing)

There are other dates, so I'm trying to convert using an ‘if’ conditional to make things a little easier, but I get the following error.

Thank you in advance.

CodePudding user response：

Check function from module datetime - isoformat or more general strftime function. These function will convert it to the expected format for you.

CodePudding user response：

Apply function iterates row by row. Do not use the lambda function inside your function date_changing.

df2['date']=df2['date'].astype(str)

def date_changing(x) :
    if len(x) == 7: return x[:6]   '0'   x[6:]
    else: return x

df2['new_date']=df2['date'].apply(date_changing)

#Another Solution would be to use pandas.to_datetime

df2['date']=df2['date'].astype(str)
df2['new_date'] = pd.to_datetime(df2['date'], format = '%Y%m%d').dt.strftime('%Y%m%d')

CodePudding user response：

Code to create the df:

import pandas as pd
from io import StringIO
d = '''
Date
2020011 
20200101
'''
df = pd.read_csv(StringIO(d))
df

Output:

    Date
0   2020011
1   20200101

Code to apply insert '0' into string:

df.applymap(lambda x: str(x) if len(str(x)) == 8 else str(x)[:6]   '0'   str(x)[6:])

Output:

Date
0   20200101
1   20200101