pandas、numpy篇——groupby

df.groupby(key)
df.groupby([key list])

grouped.sum()
分组函数
mean()  Compute mean of groups
sum()   Compute sum of group values
size()  Compute group sizes
count() Compute count of group
std()   Standard deviation of groups
var()   Compute variance of groups
sem()   Standard error of the mean of groups
describe()  Generates descriptive statistics
first() Compute first of group values
last()  Compute last of group values
nth()   Take nth value, or a subset if n is a list
min()   Compute min of group values
max()   Compute max of group values

df.agg(function list or dict)
df.transform(function)
df.apply(function)
df.applymap()
series.map()

grouped.filter(function) .filter(lambda x: x.sum() > 2)