在R data.table

Question

这个问题类似于How to change type of target column when doing := by group in a data.table in R?，但是，我需要使用.()表示法。

示例：

a <- data.table(ID = c("A", "B", "C", "A", "B", "C"), 
                TYPE = c(1, 1, 2, 2, 3, 3), 
                CLASS = c(1, 2, 3, 4, 5, 6))

b <- a[, .(Count = .N, "Failure Count" = sum(CLASS == "2"), 
       "Median DIF" = median(TYPE)), by = ID]

是否可以使用这种不同的符号来做到这一点？原因是我想创建一个新表，而不是使用:=表示法向现有表中添加一列。

Answer 1

显然，您要做的就是在as.numeric()内添加median()。

b <- a[, .(Count = .N, "Failure Count" = sum(CLASS == "2"), 
      "Median DIF" = median(as.numeric(TYPE))), by = ID]