python: how to return a DataFrame or a list from a function?

Question

This question has a big chance to be duplicated but I haven't found an answer yet. However, I'm trying to apply a function to a pandas DataFrame and I want to have a DataFrame back. Followed example is reproducible:

df = pd.DataFrame({'ID': ["1","2"],
                   'Start': datetime.strptime('20160701', '%Y%m%d'),
                   'End': datetime.strptime('20170701', '%Y%m%d'),
                   'Value': [100, 200],
                   'CreditNote': [-20, -30]})

My function:

def act_value_calc(x):
    start_delta = (x.Start.replace(day=31,month=12) - x.Start).days
    full_delta = (x.End - x.Start).days
    result1 = round( (x.Value + x.CreditNote) / full_delta * start_delta, 2)
    result2 = round( (x.Value + x.CreditNote) - result1, 2)
    return(pd.DataFrame({'r1': [result1],'r2': [result2]}))

Why I can not run the following code ...

df.apply(act_value_calc, 1)

and what should be done to let it run? I mean to get a DataFrame or a list back with result1 and result2?

Anupam khare · Accepted Answer · 2018-04-19 19:31:30Z

1

you can create a global variable by declaring it within the function and then create a data frame out of it

def act_value_calc(x): 
start_delta = (x.Start.replace(day=31,month=12) - x.Start).days
full_delta = (x.End - x.Start).days
result1 = round( (x.Value + x.CreditNote) / full_delta * start_delta, 2)
result2 = round( (x.Value + x.CreditNote) - result1, 2)
global  df ### declaring global variable
df=pd.DataFrame({'r1': [result1],'r2': [result2]})

answered Apr 19, 2018 at 19:31

Anupam khare

991 silver badge3 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

pansen · Accepted Answer · 2017-03-07 22:11:23Z

0

You can make it easier for yourself while returning a pandas.Series instead of a pandas.DataFrame:

def act_value_calc(x):
    start_delta = (x.Start.replace(day=31,month=12) - x.Start).days
    full_delta = (x.End - x.Start).days
    result1 = round( (x.Value + x.CreditNote) / full_delta * start_delta, 2)
    result2 = round( (x.Value + x.CreditNote) - result1, 2)
    return(pd.Series({'r1': result1,'r2': result2}))

print(df.apply(act_value_calc, 1))
    r1      r2
0   40.11   39.89
1   85.23   84.77

edited Mar 7, 2017 at 22:11

answered Mar 7, 2017 at 22:10

pansen

6,7034 gold badges21 silver badges33 bronze badges

1 Comment

conner.xyz Over a year ago

Ahh yeah that's solid too.

conner.xyz · Accepted Answer · 2017-03-07 22:03:27Z

apply will return some value per row, or per column, depending on the axis argument you provide (I believe you understand this already given you are providing an axis arg of 1).

Returning a DataFrame from apply is problematic. What you probably want to do is create a new column with the values returned by the function you are applying.

Something like

def act_value_calc1(x):
    start_delta = (x.Start.replace(day=31,month=12) - x.Start).days
    full_delta = (x.End - x.Start).days
    result1 = round( (x.Value + x.CreditNote) / full_delta * start_delta, 2)
    return result1

def act_value_calc2(x):
    start_delta = (x.Start.replace(day=31,month=12) - x.Start).days
    full_delta = (x.End - x.Start).days
    result2 = round( (x.Value + x.CreditNote) - x.result1, 2)
    return result2

df['result1'] = df.apply(act_value_calc1, axis=1)
df['result2'] = df.apply(act_value_calc2, axis=1)

Collectives™ on Stack Overflow

python: how to return a DataFrame or a list from a function?

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related