R由两个因素聚合

Question

假设我有data.table x：

 x <- data.table(Motif = c("A","A","B","B","B","C"),
                 Strain = c(1,1,1,2,2,3),
                 IPDRatio = c(1:6))

如何通过按因子data.table和Motif折叠整个Strain来找到IPDRatio列的平均值？

期望的输出：

   Motif Strain IPDRatio
1:     A      1      1.5
2:     B      1        3
3:     B      2      4.5
4:     C      3        6

Answer 1

这应该有效

x[, mean(IPDRatio), list(Motif, Strain)]