I think groupby
+ merge
这只是过于复杂的方法。
所以使用速度更快reindex http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.reindex.html by MultiIndex
:
mux = pd.MultiIndex.from_product([df['group'].unique(), categories], names=('group','cat'))
df = df.set_index(['group','cat']).reindex(mux).swaplevel(0,1).reset_index()
#add missing values to group column
df['group'] = df['group'].mask(df['value'].isnull())
print (df)
cat group value value2
0 a 1.0 0.0 0.0
1 b 1.0 1.0 2.0
2 c 1.0 2.0 4.0
3 d NaN NaN NaN
4 a 2.0 3.0 6.0
5 b NaN NaN NaN
6 c 2.0 4.0 8.0
7 d NaN NaN NaN
可能的解决方案:
df = df.groupby('group', group_keys=False)
.apply(lambda x: pd.merge(categories, x, how = 'outer', on='cat'))
cat group value value2
0 a 1.0 0.0 0.0
1 b 1.0 1.0 2.0
2 c 1.0 2.0 4.0
3 d NaN NaN NaN
0 a 2.0 3.0 6.0
1 b NaN NaN NaN
2 c 2.0 4.0 8.0
3 d NaN NaN NaN
Timings:
np.random.seed(123)
N = 1000000
L = list('abcd') #235,94.1,156ms
df = pd.DataFrame({'cat': np.random.choice(L, N, p=(0.002,0.002,0.005, 0.991)),
'group':np.random.randint(10000,size=N),
'value':np.random.randint(1000,size=N),
'value2':np.random.randint(5000,size=N)})
df = df.sort_values(['group','cat']).drop_duplicates(['group','cat']).reset_index(drop=True)
print (df.head(10))
categories = ['a', 'b', 'c', 'd']
def jez1(df):
mux = pd.MultiIndex.from_product([df['group'].unique(), categories], names=('group','cat'))
df = df.set_index(['group','cat']).reindex(mux, fill_value=0).swaplevel(0,1).reset_index()
df['group'] = df['group'].mask(df['value'].isnull())
return df
def jez2(df):
grouped = df.groupby('group')
categories = pd.DataFrame(['a', 'b', 'c', 'd'], columns=['cat'])
return grouped.apply(lambda x: pd.merge(categories, x, how = 'outer', on='cat'))
def coldspeed(df):
grouped = df.groupby('group')
categories = pd.DataFrame(['a', 'b', 'c', 'd'], columns=['cat'])
return pd.concat([g[1].merge(categories, how='outer', on='cat') for g in grouped])
def akilat90(df):
grouped = df.groupby('group')
categories = pd.DataFrame(['a', 'b', 'c', 'd'], columns=['cat'])
merged_list = []
for g in grouped:
merged = pd.merge(categories, g[1], how = 'outer', on='cat')
merged['group'].fillna(merged['group'].mode()[0],inplace=True) # replace the `group` column's `NA`s by mode
merged.fillna(0, inplace=True)
merged_list.append(merged)
return pd.concat(merged_list)
In [471]: %timeit jez1(df)
100 loops, best of 3: 12 ms per loop
In [472]: %timeit jez2(df)
1 loop, best of 3: 14.5 s per loop
In [473]: %timeit coldspeed(df)
1 loop, best of 3: 19.4 s per loop
In [474]: %timeit akilat90(df)
1 loop, best of 3: 22.3 s per loop