Flattening multi nested json into a pandas dataframe

Question

I'm trying to flatten this json response into a pandas dataframe to export to csv.

It looks like this:

j = [
    {
        "id": 401281949,
        "teams": [
            {
                "school": "Louisiana Tech",
                "conference": "Conference USA",
                "homeAway": "away",
                "points": 34,
                "stats": [
                    {"category": "rushingTDs", "stat": "1"},
                    {"category": "puntReturnYards", "stat": "24"},
                    {"category": "puntReturnTDs", "stat": "0"},
                    {"category": "puntReturns", "stat": "3"},
                ],
            }
        ],
    }
]

...Many more items in the stats area. If I run this and flatten to the teams level:

multiple_level_data = pd.json_normalize(j, record_path =['teams'])

I get:

           school      conference homeAway  points                                              stats
0  Louisiana Tech  Conference USA     away      34  [{'category': 'rushingTDs', 'stat': '1'}, {'ca...

How do I flatten it twice so that all of the stats are on their own column in each row?

If I do this:

multiple_level_data = pd.json_normalize(j, record_path =['teams'])
multiple_level_data = multiple_level_data.explode('stats').reset_index(drop=True)
multiple_level_data=multiple_level_data.join(pd.json_normalize(multiple_level_data.pop('stats')))

I end up with multiple rows instead of more columns:

Andrej Kesely · Accepted Answer · 2022-11-22 21:18:30Z

2

You can try:

df = pd.DataFrame(j).explode("teams")
df = pd.concat([df, df.pop("teams").apply(pd.Series)], axis=1)

df["stats"] = df["stats"].apply(lambda x: {d["category"]: d["stat"] for d in x})

df = pd.concat(
    [
        df,
        df.pop("stats").apply(pd.Series),
    ],
    axis=1,
)

print(df)

Prints:

          id          school      conference homeAway  points rushingTDs puntReturnYards puntReturnTDs puntReturns
0  401281949  Louisiana Tech  Conference USA     away      34          1              24             0           3

answered Nov 22, 2022 at 21:18

Andrej Kesely

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Comments

cottontail · Accepted Answer · 2022-11-22 22:18:48Z

can you try this:

multiple_level_data = pd.json_normalize(j, record_path =['teams'])
multiple_level_data = multiple_level_data.explode('stats').reset_index(drop=True)
multiple_level_data=multiple_level_data.join(pd.json_normalize(multiple_level_data.pop('stats')))

#convert rows to columns.
multiple_level_data=multiple_level_data.set_index(multiple_level_data.columns[0:4].to_list())
dfx=multiple_level_data.pivot_table(values='stat',columns='category',aggfunc=list).apply(pd.Series.explode).reset_index(drop=True)
multiple_level_data=multiple_level_data.reset_index().drop(['stat','category'],axis=1).drop_duplicates().reset_index(drop=True)
multiple_level_data=multiple_level_data.join(dfx)

Output:

	school	conference	homeAway	points	puntReturnTDs	puntReturnYards	puntReturns	rushingTDs
0	Louisiana Tech	Conference USA	away	34	0	24	3	1

cottontail · Accepted Answer · 2022-11-22 22:11:11Z

Instead of calling explode() on an output of a json_normalize(), you can explicitly pass the paths to the meta data for each column in a single json_normalize() call. For example, ['teams', 'school'] would be one path, ['teams', 'conference'] is another path, etc. This will create a long dataframe similar to what you already have.

Then you can call pivot() to reshape this output into the correct shape.

# normalize json
df = pd.json_normalize(
    j, record_path=['teams', 'stats'], 
    meta=['id', *(['teams', c] for c in ('school', 'conference', 'homeAway', 'points'))]
)
# column name contains 'teams' prefix; remove it
df.columns = [c.split('.')[1] if '.' in c else c for c in df]

# pivot the intermediate result
df = (
    df.astype({'points': int, 'id': int})
    .pivot(['id', 'school', 'conference', 'homeAway', 'points'], 'category', 'stat')
    .reset_index()
)
# remove index name
df.columns.name = None
df

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