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How do you convert a given dataframe with a hierarchical structure and arbitrary shape (say, similar to the one below) into a new dataframe with a parent and child column?

data = {'level1': ['A', 'A', 'B', 'B', 'C'],
        'level2': ['James', 'Robert', 'Patricia', 'Patricia', 'John'],
        'level3': ['Stockholm', 'Denver', 'Moscow', 'Moscow', 'Palermo'],
        'level4': ['red', 'Denver', 'yellow', 'purple', 'blue']
        }

df = pd.DataFrame(data)

  level1    level2     level3  level4
0      A     James  Stockholm     red
1      A    Robert     Denver  Denver
2      B  Patricia     Moscow  yellow
3      B  Patricia     Moscow  purple
4      C      John    Palermo    blue

Desired output is something like this:

       parent      child
0           A      James
1           A     Robert
2           B   Patricia
3           C       John
4       James  Stockholm
5      Robert     Denver
6    Patricia     Moscow
7        John    Palermo
8   Stockholm        red
9      Moscow     yellow
10     Moscow     purple
11    Palermo       blue

How do you convert a given dataframe with a hierarchical structure and arbitrary shape (say, similar to the one below) into a new dataframe with a parent and child column?

Edit: Note that a constraint is that a child cannot be its own parent.

data = {'level1': ['A', 'A', 'B', 'B', 'C'],
        'level2': ['James', 'Robert', 'Patricia', 'Patricia', 'John'],
        'level3': ['Stockholm', 'Denver', 'Moscow', 'Moscow', 'Palermo'],
        'level4': ['red', 'Denver', 'yellow', 'purple', 'blue']
        }

df = pd.DataFrame(data)

  level1    level2     level3  level4
0      A     James  Stockholm     red
1      A    Robert     Denver  Denver
2      B  Patricia     Moscow  yellow
3      B  Patricia     Moscow  purple
4      C      John    Palermo    blue

Desired output is something like this:

       parent      child
0           A      James
1           A     Robert
2           B   Patricia
3           C       John
4       James  Stockholm
5      Robert     Denver
6    Patricia     Moscow
7        John    Palermo
8   Stockholm        red
9      Moscow     yellow
10     Moscow     purple
11    Palermo       blue

How do you convert a given dataframe with a hierarchical structure and arbitrary shape (say, similar to the one below) into a new dataframe with a parent and child column?

data = {'level1': ['A', 'A', 'B', 'B', 'C'],
        'level2': ['James', 'Robert', 'Patricia', 'Patricia', 'Patricia'],
        'level3': ['Stockholm', 'Denver', 'Moscow', 'Moscow', 'Palermo'],
        'level4': ['red', 'Denver', 'yellow', 'purple', 'blue']
        }

df = pd.DataFrame(data)

  level1    level2     level3  level4
0      A     James  Stockholm     red
1      A    Robert     Denver  Denver
2      B  Patricia     Moscow  yellow
3      B  Patricia     Moscow  purple
4      C      John    Palermo    blue

Desired output is something like this:

       parent      child
0           A      James
1           A     Robert
2           B   Patricia
3           C       John
4       James  Stockholm
5      Robert     Denver
6    Patricia     Moscow
7        John    Palermo
8   Stockholm        red
9      Moscow     yellow
10     Moscow     purple
11    Palermo       blue

How do you convert a given dataframe with a hierarchical structure and arbitrary shape (say, similar to the one below) into a new dataframe with a parent and child column?

data = {'level1': ['A', 'A', 'B', 'B', 'C'],
        'level2': ['James', 'Robert', 'Patricia', 'Patricia', 'John'],
        'level3': ['Stockholm', 'Denver', 'Moscow', 'Moscow', 'Palermo'],
        'level4': ['red', 'Denver', 'yellow', 'purple', 'blue']
        }

df = pd.DataFrame(data)

  level1    level2     level3  level4
0      A     James  Stockholm     red
1      A    Robert     Denver  Denver
2      B  Patricia     Moscow  yellow
3      B  Patricia     Moscow  purple
4      C      John    Palermo    blue

Desired output is something like this:

       parent      child
0           A      James
1           A     Robert
2           B   Patricia
3           C       John
4       James  Stockholm
5      Robert     Denver
6    Patricia     Moscow
7        John    Palermo
8   Stockholm        red
9      Moscow     yellow
10     Moscow     purple
11    Palermo       blue

How do you convert a given dataframe with a hierarchical structure and arbitrary shape (say, similar to the one below) into a new dataframe with a parent and child column?

data = {'level1': ['A', 'A', 'B', 'B', 'C'],
        'level2': ['James', 'Robert', 'Patricia', 'Patricia', 'Patricia'],
        'level3': ['Stockholm', 'Denver', 'Moscow', 'Moscow', 'Palermo'],
        'level4': ['red', 'Denver', 'yellow', 'purple', 'blue']
        }

df = pd.DataFrame(data)

  level1    level2     level3  level4
0      A     James  Stockholm     red
1      A    Robert     Denver  Denver
2      B  Patricia     Moscow  yellow
3      B  Patricia     Moscow  purple
4      C  Patricia    Palermo    blue

How do you convert a given dataframe with a hierarchical structure and arbitrary shape (say, similar to the one below) into a new dataframe with a parent and child column?

data = {'level1': ['A', 'A', 'B', 'B', 'C'],
        'level2': ['James', 'Robert', 'Patricia', 'Patricia', 'Patricia'],
        'level3': ['Stockholm', 'Denver', 'Moscow', 'Moscow', 'Palermo'],
        'level4': ['red', 'Denver', 'yellow', 'purple', 'blue']
        }

df = pd.DataFrame(data)

  level1    level2     level3  level4
0      A     James  Stockholm     red
1      A    Robert     Denver  Denver
2      B  Patricia     Moscow  yellow
3      B  Patricia     Moscow  purple
4      C      John    Palermo    blue

Desired output is something like this:

       parent      child
0           A      James
1           A     Robert
2           B   Patricia
3           C       John
4       James  Stockholm
5      Robert     Denver
6    Patricia     Moscow
7        John    Palermo
8   Stockholm        red
9      Moscow     yellow
10     Moscow     purple
11    Palermo       blue