How to Unnest List Columns in Pandas DataFrames?

Unnesting Columns with Pandas

When dealing with DataFrames that contain columns of lists, it can be useful to "unfold" these lists into separate rows.

Method 1: Using DataFrame.explode() (Pandas >= 0.25)

For single-column explosion, use explode() directly:

df = pd.DataFrame({'A': [1, 2], 'B': [[1, 2], [1, 2]]})

df_exploded = df.explode('B')

Method 2: Apply Series

df_exploded = df.set_index('A').B.apply(pd.Series).stack().reset_index(level=0).rename(columns={0:'B'})

Method 3: Repeat DataFrame

df_exploded = pd.DataFrame({'A':df.A.repeat(df.B.str.len()),'B':np.concatenate(df.B.values)})

Method 4: Reindex/Loc

df_exploded = df.reindex(df.index.repeat(df.B.str.len())).assign(B=np.concatenate(df.B.values))

Method 5: ChainMap

from collections import ChainMap
d = dict(ChainMap(*map(dict.fromkeys, df['B'], df['A'])))
df_exploded = pd.DataFrame(list(d.items()),columns=df.columns[::-1])

Method 6: Numpy

newvalues=np.dstack((np.repeat(df.A.values,list(map(len,df.B.values))),np.concatenate(df.B.values)))
df_exploded = pd.DataFrame(data=newvalues[0],columns=df.columns)

Method 7: Iterators

from itertools import cycle,chain
l=df.values.tolist()
l1=[list(zip([x[0]], cycle(x[1])) if len([x[0]]) > len(x[1]) else list(zip(cycle([x[0]]), x[1]))) for x in l]
df_exploded = pd.DataFrame(list(chain.from_iterable(l1)),columns=df.columns)

Generalization to Multiple Columns

To generalize the above methods for multiple columns, use the following function:

def unnesting(df, explode):
    idx = df.index.repeat(df[explode[0]].str.len())
    df1 = pd.concat([
        pd.DataFrame({x: np.concatenate(df[x].values)}) for x in explode], axis=1)
    df1.index = idx
    
    return df1.join(df.drop(explode, 1), how='left')

Column-Wise Unnesting

To unnest horizontally, modify the function:

def unnesting(df, explode, axis):
    if axis==1:
        # Previous implementation
    else :
        df1 = pd.concat([
                         pd.DataFrame(df[x].tolist(), index=df.index).add_prefix(x) for x in explode], axis=1)
        return df1.join(df.drop(explode, 1), how='left')

The above is the detailed content of How to Unnest List Columns in Pandas DataFrames?. For more information, please follow other related articles on the PHP Chinese website!