Rbind with new columns and data.table

Question

I need to add many large tables to an existing table, so I use rbind with the excellent package data.table. But some of the later tables have more columns than the original

Answer 1

Here is an approach that will update the missing columns in

rbind.missing <- function(A, B) { 

  cols.A <- names(A)
  cols.B <- names(B)

  missing.A <- setdiff(cols.B,cols.A)
  # check and define missing columns in A
  if(length(missing.A) > 0L){
   # .. means "look up one level"
   class.missing.A <- lapply(B[, ..missing.A], class)
   nas.A <- lapply(class.missing.A, as, object = NA)
   A[,c(missing.A) := nas.A]
  }
  # check and define missing columns in B
  missing.B <- setdiff(names(A), cols.B)
  if(length(missing.B) > 0L){
    class.missing.B <- lapply(A[, ..missing.B], class)
    nas.B <- lapply(class.missing.B, as, object = NA)
    B[,c(missing.B) := nas.B]
  }
  # reorder so they are the same
  setcolorder(B, names(A))
  rbind(A, B)

}

rbind.missing(dt.1,dt.2)

##    aa bb cc
## 1:  1  2 NA
## 2:  2  3 NA
## 3:  3  4 NA
## 4:  1  2  3
## 5:  2  3  4
## 6:  3  4  5

This will not be efficient for many, or large data.tables, as it only works two at a time.