create a dictionary in python from columns of a dataframe

Question

I have the below sample data:

class   name
Pref    Ab
Val     BE
Base    es
Pref    Cw
Base    SS

This data is in a dataframe and I need to create a mapping for class : name as shown below:

Pref : ['Ab','Cw'],
Val  : ['BE'],
Base : ['es','SS']

This will be a dictionary which will contain a mapping for class and it's component names.The key will be class and it's values will be the names in that class, so a list of values for each class, where the list length might vary for each class. Can someone please help me with this?

cs95 · Accepted Answer · 2018-01-01 06:59:13Z

1

You'd be looking for a groupby + to_dict operation -

r = df.groupby('class').name.apply(list).to_dict()

Or,

r = df.groupby('class').name.agg(pd.Series.tolist).to_dict()

r
{'Base': ['es', 'SS'], 'Pref': ['Ab', 'Cw'], 'Val': ['BE']}

How it works -

The class column consists of 3 categories. We want each category as an index.
Furthermore, each element in the name column would need to be grouped by class and present in a list

It follows that a groupby operation is the most straightforward thing to do here. Group and apply/aggregate with list to get a series with index as so -

class
Base    [es, SS]
Pref    [Ab, Cw]
Val         [BE]
Name: name, dtype: object

Calling to_dict on this gives you what you want.

edited Jan 1, 2018 at 6:59

answered Jan 1, 2018 at 6:53

cs95

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