刚遇到一个问题，就是分组求和在R里怎么实现比较简便？

对应SQL语句为：SELECT customer, sum(consumption) FROM consume group by customer

然后就是类似的，分组计数怎么做？

a=data.frame(customer=c('a','b','a','m','a','b'),consumption=1:6)a  customer consumption1        a           12        b           23        a           34        m           45        a           56        b           6tapply(a$consumption,a$customer,sum)a b m9 8 4tapply(a$consumption,a$customer,length)a b m3 2 1

　　

在搞复杂点。

a=data.frame(customer=c('a','b','a','m','a','b'),consumption=1:6,groups=c('A','B','A','B','A','B'))aggregate(a$consumption, list(a$customer,a$groups), sum) Group.1 Group.2 x1       a       A 92       b       B 83       m       B 4library(data.table)consume<-data.table(consume)setkey(consume,customer)a1<-consume[,sum(consumption),customer]