Repeat headers when using xtable with longtable option

Question

Is there a way to repeat the top row / set headers when generating an xtable with a longtable option ?

For eg., if I have

tableSb <- xtable(df, caption="A Very Long Table", label="ALongTable")
print(tableSb, include.rownames=TRUE, tabular.environment="longtable", floating=FALSE)

This works fine, but when the tables roll over into a new page the headers are not repeated. Any suggestions ?

Answer 1

In order to accomplish this, you'll need to use the add.to.row option of the print function (run ?print.xtable for more information).

Try this (adapted from https://r-forge.r-project.org/tracker/?func=detail&atid=4864&aid=1627&group_id=1228)

addtorow          <- list()
addtorow$pos      <- list()
addtorow$pos[[1]] <- c(0)
addtorow$command  <- c(paste(
  "\\hline \n",
  "\\endhead \n",
  "\\hline \n",
  "{\\footnotesize Continued on next page} \n",
  "\\endfoot \n",
  "\\endlastfoot \n",
  sep=""))
x.big <- xtable(
  x,
  label = "tabbig",
  caption = "Example of longtable spanning several pages")
print(
  x.big,
  tabular.environment = "longtable",
  floating = FALSE,
  include.rownames = FALSE,  # because addtorow will substitute the default row names 
  add.to.row = addtorow,     # this is where you actually make the substitution
  hline.after=c(-1))         # because addtorow will substitute the default hline for the first row

It's a bit clumsy of a solution, but at least it'll provide you with plenty of customization.

Answer 2

Looking at the code for print.xtable, the only considerations it makes when tabular.environment="longtable" are

• Emitting a warning if you also set floating=TRUE
• Putting the caption in the right place for a longtable (top or bottom)

It does not emit the code specific for repeating the headers on subsequent pages. Check out latex in the Hmisc package. I know it has support for longtables as well, but I don't recall if it repeats headers correctly.