Pandas DataFrame.groupby() to dictionary with multiple columns for value

Question

type(Table)
pandas.core.frame.DataFrame

Table
======= ======= =======
Column1 Column2 Column3
0       23      1
1       5       2
1       2       3
1       19      5
2       56      1
2       22      2
3       2       4
3       14      5
4       59      1
5       44      1
5       1       2
5       87      3

For anyone familliar with pandas how would I build a multivalue dictionary with the .groupby() method?

I would like an output to resemble this format:

{
    0: [(23,1)]
    1: [(5,  2), (2, 3), (19, 5)]
    # etc...
    }

where Col1 values are represented as keys and the corresponding Col2 and Col3 are tuples packed into an array for each Col1 key.

My syntax works for pooling only one column into the .groupby():

Table.groupby('Column1')['Column2'].apply(list).to_dict()
# Result as expected
{
    0: [23], 
    1: [5, 2, 19], 
    2: [56, 22], 
    3: [2, 14], 
    4: [59], 
    5: [44, 1, 87]
}

However specifying multiple values for the indices results in returning column names for the value :

Table.groupby('Column1')[('Column2', 'Column3')].apply(list).to_dict()
# Result has column namespace as array value
{
    0: ['Column2', 'Column3'],
    1: ['Column2', 'Column3'],
    2: ['Column2', 'Column3'],
    3: ['Column2', 'Column3'],
    4: ['Column2', 'Column3'],
    5: ['Column2', 'Column3']
 }

How would I return a list of tuples in the value array?

Answer 1

Customize the function you use in apply so it returns a list of lists for each group:

df.groupby('Column1')[['Column2', 'Column3']].apply(lambda g: g.values.tolist()).to_dict()
# {0: [[23, 1]], 
#  1: [[5, 2], [2, 3], [19, 5]], 
#  2: [[56, 1], [22, 2]], 
#  3: [[2, 4], [14, 5]], 
#  4: [[59, 1]], 
#  5: [[44, 1], [1, 2], [87, 3]]}

If you need a list of tuples explicitly, use list(map(tuple, ...)) to convert:

df.groupby('Column1')[['Column2', 'Column3']].apply(lambda g: list(map(tuple, g.values.tolist()))).to_dict()
# {0: [(23, 1)], 
#  1: [(5, 2), (2, 3), (19, 5)], 
#  2: [(56, 1), (22, 2)], 
#  3: [(2, 4), (14, 5)], 
#  4: [(59, 1)], 
#  5: [(44, 1), (1, 2), (87, 3)]}