在数据集中查找唯一组合

Question

我有以下数据集：

library(data.table)

dt1 <- data.table(Activity1 = c("A","A","B","B","C","C"),
                  Activity2 = c("B","C","A","C","A","B"),
                  participants = c(12, 22, 4, 20, 3, 31))

# OUTPUT (dt1)
# Activity1 Activity2 participants
# 1:         A         B           12
# 2:         A         C           22
# 3:         B         A            4
# 4:         B         C           20
# 5:         C         A            3
# 6:         C         B           31

我试图找到Activity1和Activity2的所有独特组合，这样我最终会得到一个如下所示的数据集（总结潜在的参与者）：

# DESIRED Dataset
#    Activity1 Activity2 participants
# 1:         A         B           16
# 2:         A         C           25
# 4:         B         C           51

我对R来说还是比较新的，并且会感激任何指导。 提前谢谢。