按组累计 [英] cumsum by group

问题描述

假设数据看起来像

group1 group2 num
A      sg     1
A      sh     2
A      sg     4
B      at     3
B      al     7

a <- cumsum(data[,"num"]) # 1 3 7 10 17

我需要一些团体积累的东西.实际上，我有多个列作为分组指标.我想得到我定义的子组的累计总和.

I need something accumulated by groups. In reality,I have multiple columns as grouping indicators. I want to get the accumulated sum by the subgroup I define.

例如

如果我只按group1分组，那么输出应该是

If I group by group1 only, then the output should be

group1 sum
A      1
A      3
A      7
B      3
B      10

如果我按两个变量分组 group1,group2 那么输出是

If I group by two variables group1,group2 then the output is

group1 group2 sum
A      sg     1
A      sh     2
A      sg     5
B      at     3
B      al     7

推荐答案

library(data.table)

data <- data.table(group1=c('A','A','A','B','B'),sum=c(1,2,4,3,7))

data[,list(cumsum = cumsum(sum)),by=list(group1)]

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