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pythonpandasdataframemean

How to get average/mean with mapping in pandas dataframe?

I have a dataframe that looks something like this:

Birthyear Weight
1992 2
1993 2.2
1992 3
1993 2.5
1994 2.4
1993 1.8
1994 2.1

Note: This is an example, I have +100k of rows and years

I want to get a new DataFrame in which I have every year and its average weight, mapping automatically every year because it would take a lot of work and code lines to do it manually.

Birthyear Weight
1992 2.5
1993 2.1
1994 2.25

I've tried mapping, which worked before to use a reference table, but didn't work for this

dfaverage = df

dfaverage['Weight'] = dfaverage['Birthyear'].map(df.set_index('Year')[df['Weight'].mean])

TypeError: unhashable type: 'DataFrame'

Any ideas on how can I make this idea work?

Solution

  • Use a groupby:

    dfaverage.groupby('Birthyear')['Weight'].mean().to_frame()