R package xtable, how to create a latextable with multiple rows and columns from R

Question

My goal is to create latextable with multirow/multicolumn features from R. The latextable I want should look like this:

               colLabel  |  colLabel2
                         |
                 a1  a2  |   a3    a4  
 -------------------------------------
             b1  1    2  |   5     6
 rowLabel1               |
             b2  3    4  |   7     8
 --------------------------------------
             b3  9   10  |   13    14
 rowLabel2               |
             b4  11  12  |   15    16
 --------------------------------------

I am currently using xtable but I cannot figure out how to create multirow using this package. Could anyone tell me how to create such table?

Thank you in advance

Answer 1

I just would like to point at a combination of Christoph's block entry (here) and Gabor's answer in the R mail list (here) working with the xtable package. Furthermore, this solution is capable of merging cells in the \multirow manner.

Here comes a MWE:

require(xtable)

# set up data frame
df <- data.frame(c(replicate(2, c("L1")), replicate(2, c("L2"))),
                 replicate(4, "b"),
                 replicate(4, runif(4, 1, 10)) )

# only needed if first column consists of numbers
df[[1]] <- as.character(df[[1]])

rle.lengths <- rle(df[[1]])$lengths
first <- !duplicated(df[[1]])
df[[1]][!first] <- ""

# define appearance of \multirow
df[[1]][first] <-
   paste0("\\midrule\\multirow{", rle.lengths, "}{*}{\\textbf{", df[[1]][first], "}}")

strCaption <- paste0("\\textbf{Table Whatever} This table is just produced with some ",
                     "random data and does not mean anything. Just to show you how ",
                     "things work.")

# set up xtable output
print(xtable(df, digits = c(0, 0, 0, 3, 1, 0, 6), # first zero "represents" row numbers which we skip later
             align = "lllrr|rr",  # align and put a vertical line (first "l" again represents column of row numbers)
             caption = strCaption, label = "testTable"),
      size = "footnotesize", #Change size; useful for bigger tables "normalsize" "footnotesize"
      include.rownames = FALSE, #Don't print rownames
      include.colnames = FALSE, #We create them ourselves
      caption.placement = "top", #"top", NULL
      hline.after=NULL, #We don't need hline; we use booktabs
      floating=TRUE, # whether \begin{Table} should be created (TRUE) or not (FALSE)
      sanitize.text.function = force, # Important to treat content of first column as latex function
      add.to.row = list(pos = list(-1,
                                   2,
                                   nrow(df)),
                        command = c(paste("\\toprule \n",  # NEW row
                                          "\\multicolumn{2}{c}{} & \\multicolumn{2}{c}{\\textbf{colLabel1}} & \\multicolumn{2}{c}{colLabel2} \\\\\n",
                                          "\\cmidrule(l){3-4} \\cmidrule(l){5-6}\n",
                                          " & & a1 & a2 & a3 & a4 \\\\\n", # NEW row 
                                          "\\midrule \n"
                                          ),
                                    paste("\\cmidrule(l){3-4} \\cmidrule(l){5-6}\n" # we may also use 'pos' and 'command' to add a midrule
                                          ),
                                    paste("\\bottomrule \n"  # paste is used as it is more flexible regarding adding lines
                                          )
                                    )
                        )
      )

Which knits the following table in LaTeX: