R data.table: 重用一个聚合

Question

我想对多个数据表应用相同的聚合，而不重写聚合方案。

考虑

dt1 <- data.table(id = c(1,2), a = rnorm(10), b = rnorm(10), c = rnorm(10))
dt2 <- data.table(id = c(1,2), a = rnorm(10), b = rnorm(10), c = rnorm(10))

dt1_aggregates <- dt1[, .(mean_a=mean(a), sd_a=sd(a), mean_b=mean(b), sd_b=sd(b)), by=id]
dt2_aggregates <- dt2[, .(mean_a=mean(a), sd_a=sd(a), mean_b=mean(b), sd_b=sd(b)), by=id]

有没有什么方法可以为 dt2 重用 dt1_aggregates 聚合方案而不必将其写出两次？

Answer 1

您可以引用您想要的表达式，然后在 data.table:

中计算它

my.call=quote(list(mean_a=mean(a), sd_a=sd(a), mean_b=mean(b), sd_b=sd(b)))
dt1[, eval(my.call), by=id]

生产

   id       mean_a      sd_a      mean_b      sd_b
1:  1  0.004165423 0.7504691 -0.05001424 1.4440434
2:  2 -0.430910188 0.9648096  0.26918995 0.8680997

和

dt2[, eval(my.call), by=id]

生产

   id     mean_a     sd_a     mean_b      sd_b
1:  1  0.2974145 1.191863 -0.0588854 0.7896988
2:  2 -0.4642856 1.438937  0.3612607 1.0581702

R data.table: 重用一个聚合

R data.table: reuse an aggregation

r

expression

data.table

aggregate

quoting