按组累计 [英] Cumulative total by group

问题描述

对于以下数据集：

d = data.frame(date = as.Date(as.Date('2015-01-01'):as.Date('2015-04-10'), origin = "1970-01-01"),
               group = rep(c('A','B','C','D'), 25), value = sample(1:100))
head(d)
         date group value
1: 2015-01-01     A     4
2: 2015-01-02     B    32
3: 2015-01-03     C    46
4: 2015-01-04     D    40
5: 2015-01-05     A    93
6: 2015-01-06     B    10

..谁能建议一个更优雅的人比此 data.table ）方法按组计算累积值总数的方法？

.. can anyone advise a more elegant way to calculate a cumulative total of values by group than this data.table) method?

library(data.table)
setDT(d)
d.cast = dcast.data.table(d, group ~ date, value.var = 'value', fun.aggregate = sum)
c.sum = d.cast[, as.list(cumsum(unlist(.SD))), by = group]

..这很笨重，会产生需要 dplyr :: gather 或 reshape2 :: melt 重新格式化。

.. which is pretty clunky and yields a flat matrix that needs dplyr::gather or reshape2::melt to reformat.

当然，R可以做得比这更好？？

Surely R can do better than this??

推荐答案

如果您只希望每个组的累加总和，那么您可以做

If you just want cumulative sums per group, then you can do

transform(d, new=ave(value,group,FUN=cumsum))

以R为基

这篇关于按组累计的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！