聚合 data.table 中的多个列 [英] aggregating multiple columns in data.table

问题描述

我有以下示例 data.table:

dtb <- data.table(a=sample(1:100,100), b=sample(1:100,100), id=rep(1:10,10))

例如，我想使用 colSums 按 id 聚合所有列(a 和 b，尽管它们应该分开).这样做的正确方法是什么?以下方法不起作用:

I would like to aggregate all columns (a and b, though they should be kept separate) by id using colSums, for example. What is the correct way to do this? The following does not work:

 dtb[,colSums, by="id"]

这只是一个示例，我的表有很多列，所以我想避免在函数名中指定所有列

This is just a sample and my table has many columns so I want to avoid specifying all of them in the function name

推荐答案

这实际上是我一直在寻找的，并且在常见问题解答中提到:

this is actually what i was looking for and is mentioned in the FAQ:

dtb[,lapply(.SD,mean),by="id"]

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