How to one-hot-encode from a pandas column containing a list?
We can also use sklearn.preprocessing.MultiLabelBinarizer:
Often we want to use sparse DataFrame for the real world data in order to save a lot of RAM.
Sparse solution (for Pandas v0.25.0+)
from sklearn.preprocessing import MultiLabelBinarizer
mlb = MultiLabelBinarizer(sparse_output=True)
df = df.join(
pd.DataFrame.sparse.from_spmatrix(
mlb.fit_transform(df.pop('Col3')),
index=df.index,
columns=mlb.classes_))
result:
In [38]: df
Out[38]:
Col1 Col2 Apple Banana Grape Orange
0 C 33.0 1 1 0 1
1 A 2.5 1 0 1 0
2 B 42.0 0 1 0 0
In [39]: df.dtypes
Out[39]:
Col1 object
Col2 float64
Apple Sparse[int32, 0]
Banana Sparse[int32, 0]
Grape Sparse[int32, 0]
Orange Sparse[int32, 0]
dtype: object
In [40]: df.memory_usage()
Out[40]:
Index 128
Col1 24
Col2 24
Apple 16 # <--- NOTE!
Banana 16 # <--- NOTE!
Grape 8 # <--- NOTE!
Orange 8 # <--- NOTE!
dtype: int64
Dense solution
mlb = MultiLabelBinarizer()
df = df.join(pd.DataFrame(mlb.fit_transform(df.pop('Col3')),
columns=mlb.classes_,
index=df.index))
Result:
In [77]: df
Out[77]:
Col1 Col2 Apple Banana Grape Orange
0 C 33.0 1 1 0 1
1 A 2.5 1 0 1 0
2 B 42.0 0 1 0 0
Option 1
Short Answerpir_slow
df.drop('Col3', 1).join(df.Col3.str.join('|').str.get_dummies())
Col1 Col2 Apple Banana Grape Orange
0 C 33.0 1 1 0 1
1 A 2.5 1 0 1 0
2 B 42.0 0 1 0 0
Option 2
Fast Answerpir_fast
v = df.Col3.values
l = [len(x) for x in v.tolist()]
f, u = pd.factorize(np.concatenate(v))
n, m = len(v), u.size
i = np.arange(n).repeat(l)
dummies = pd.DataFrame(
np.bincount(i * m + f, minlength=n * m).reshape(n, m),
df.index, u
)
df.drop('Col3', 1).join(dummies)
Col1 Col2 Apple Orange Banana Grape
0 C 33.0 1 1 1 0
1 A 2.5 1 0 0 1
2 B 42.0 0 0 1 0
Option 3pir_alt1
df.drop('Col3', 1).join(
pd.get_dummies(
pd.DataFrame(df.Col3.tolist()).stack()
).astype(int).sum(level=0)
)
Col1 Col2 Apple Orange Banana Grape
0 C 33.0 1 1 1 0
1 A 2.5 1 0 0 1
2 B 42.0 0 0 1 0
Timing Results
Code Below
def maxu(df):
mlb = MultiLabelBinarizer()
d = pd.DataFrame(
mlb.fit_transform(df.Col3.values)
, df.index, mlb.classes_
)
return df.drop('Col3', 1).join(d)
def bos(df):
return df.drop('Col3', 1).assign(**pd.get_dummies(df.Col3.apply(lambda x:pd.Series(x)).stack().reset_index(level=1,drop=True)).sum(level=0))
def psi(df):
return pd.concat([
df.drop("Col3", 1),
df.Col3.apply(lambda x: pd.Series(1, x)).fillna(0)
], axis=1)
def alex(df):
return df[['Col1', 'Col2']].assign(**{fruit: [1 if fruit in cell else 0 for cell in df.Col3]
for fruit in set(fruit for fruits in df.Col3
for fruit in fruits)})
def pir_slow(df):
return df.drop('Col3', 1).join(df.Col3.str.join('|').str.get_dummies())
def pir_alt1(df):
return df.drop('Col3', 1).join(pd.get_dummies(pd.DataFrame(df.Col3.tolist()).stack()).astype(int).sum(level=0))
def pir_fast(df):
v = df.Col3.values
l = [len(x) for x in v.tolist()]
f, u = pd.factorize(np.concatenate(v))
n, m = len(v), u.size
i = np.arange(n).repeat(l)
dummies = pd.DataFrame(
np.bincount(i * m + f, minlength=n * m).reshape(n, m),
df.index, u
)
return df.drop('Col3', 1).join(dummies)
results = pd.DataFrame(
index=(1, 3, 10, 30, 100, 300, 1000, 3000),
columns='maxu bos psi alex pir_slow pir_fast pir_alt1'.split()
)
for i in results.index:
d = pd.concat([df] * i, ignore_index=True)
for j in results.columns:
stmt = '{}(d)'.format(j)
setp = 'from __main__ import d, {}'.format(j)
results.set_value(i, j, timeit(stmt, setp, number=10))
You can use the functions explode (new in version 0.25.0.) and crosstab:
s = df['Col3'].explode()
df[['Col1', 'Col2']].join(pd.crosstab(s.index, s))
Output:
Col1 Col2 Apple Banana Grape Orange
0 C 33.0 1 1 0 1
1 A 2.5 1 0 1 0
2 B 42.0 0 1 0 0