R data.table 按组计算多列中的唯一值

Question

> require(data.table)
> have <- data.table(ID = c(1,1,1,2,2)
+                      , colA = c("A","B","A","A","A")
+                      , colB = c("C","A","B","B","C"))
> have
   ID colA colB
1:  1    A    C
2:  1    B    A
3:  1    A    B
4:  2    A    B
5:  2    A    C
> want <- data.table(ID = c(1,2), UnN = c(3,3))
> want
   ID UnN
1:  1   3
2:  2   3

我有一个数据表“有”，我想按组“ID”计算多个列“colA”和“colB”中的唯一值。如何实现？

不确定为什么以下内容不起作用:

have[, UnN = uniqueN(c("colA","colB")), by = C("ID")]

Answer 1

删除列名称周围的引号，以便列可以在传递给 uniqueN 函数之前被评估为向量，否则它们被评估为文字字符向量:

have[, .(UnN = uniqueN(c(colA, colB))), ID]
#   ID UnN
#1:  1   3
#2:  2   3