sort_values

(dogs[dogs['size'] == 'medium']
 .sort_values('type')
 .groupby('type').median()
)
执行步骤：

selecting a column

dogs['longevity']

dogs.groupby('size').mean()
执行步骤：

dogs.groupby(['type', 'size'])

(dogs
  .sort_values('size')
  .groupby('size')['height']
  .agg(['sum', 'mean', 'std'])
)
执行步骤

df.loc[:, df.loc['two'] <= 20]

dogs.loc[(dogs['size'] == 'medium') & (dogs['longevity'] > 12), 'breed']

dogs.drop(columns=['type'])

ppl.join(dogs)

ppl.merge(dogs, left_on='likes', right_on='breed', how='left')

dogs.pivot_table(index='size', columns='kids', values='price')

dogs.melt()

dogs.pivot(index='size', columns='kids')

dogs.stack()

dogs.unstack()

dogs.reset_index()

dogs.set_index('breed')