I need to do matrix multiplication inside a data.table. Like this
DT1 <- data.table( x = rnorm(100), y = rnorm(100))
DT2 <- data.table(z = rt(100,3))
DT3 <- data.table::data.table( a = list(DT1,DT2))
In a simple DT1, I know by using
DT1[, x %*% t(x)]
can ouput a matrix.
However, when DT1,DT2 are wrapped in DT3, if I want to compute x %*% t(z), how can I do it? Thanks
Perhaps you can try Map + tcrossprod within DT3 like below
DT3[, do.call(tcrossprod, Map(`[[`, a, c("x", "z")))]
We can loop over the list column with lapply, extract the dataset first column and apply the %*%
DT3[, lapply(a, function(u) u[[1]] %*% t(u[[1]]))]
If the OP wanted to do this based on extracting the list elements
DT3[, a[[1]]$x %*% t(a[[2]]$z)]