CODEWITHSUNDEEP
pythonpandasmulti-index
havingaball
havingaball

Reputation: 378

Using functions on multi-indexed dataframe

I think this is a basic question but I have not been able to find a usable solution yet. I have some data that is multi-index by month and year as in this attached figure dataframe I want to do some transformations on some columns for each year and month. Let's say I have some function:

def foo(series):
   return series/series.max()

So I would like to apply this function to some column (say, vol) for every month of every year, rather than for all the data at once. Can someone help?

Upvotes: 1

Views: 22

Answers (1)

jezrael
jezrael

Reputation: 863156

You can use GroupBy.transform, because function return Series:

df['new'] = df.groupby(['year','month'])['vol'].transform(foo)

Alternative here is:

df['new'] = df['vol'].div(df.groupby(['year','month'])['vol'].transform('max'))

Upvotes: 1

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