r - 将矩阵分配给 data.table 的子集

Question

我想将矩阵分配给 data.table 的多列子集但矩阵最终被视为列向量。例如，

dt1 <- data.table(a1=rnorm(5), a2=rnorm(5), a3=rnorm(5))
m1 <- matrix(rnorm(10), ncol=2)
dt1[,c("a1","a2")] <- m1

Warning messages:
1: In `[<-.data.table`(`*tmp*`, , c("a1", "a2"), value = c(-0.308851784175091,  :
  2 column matrix RHS of := will be treated as one vector
2: In `[<-.data.table`(`*tmp*`, , c("a1", "a2"), value = c(-0.308851784175091,  :
  Supplied 10 items to be assigned to 5 items of column 'a1' (5 unused)
3: In `[<-.data.table`(`*tmp*`, , c("a1", "a2"), value = c(-0.308851784175091,  :
  2 column matrix RHS of := will be treated as one vector
4: In `[<-.data.table`(`*tmp*`, , c("a1", "a2"), value = c(-0.308851784175091,  :
  Supplied 10 items to be assigned to 5 items of column 'a2' (5 unused)

问题可以先转换 m1解决成为另一个 data.table对象，但我很好奇这个错误的原因是什么。如果 dt1，上述语法将起作用是 data.frame ;不使用它的架构原理是什么 data.table ?

Answer 1

dt1[,c("a1","a2")] <- as.data.table(m1)

给出了一个简单的解决方案，但确实复制了一份。

@Simon O'Hanlon 在 data.table 中提供了解决方案道路:

dt1[ , `:=`( a1 = m1[,1] , a2 = m1[,2] ) ]

在我看来更好 data.table解决方案由@Frank 提供:

dt1[,c("a1","a2") := as.data.table(m1)]