R: xtable caption (or comment)

Question

I want to put a comment under a table printed out by xtable. I figured that the best option would be to use the "caption" option: xtable(tablename, caption="This is a caption"). But this is somehow putting in a "Table 1" automatically, so that the output looks like:

Table 1: This is a caption.

Is there any way to suppress this or any simpler way of putting in a comment simply as an additional last row in the table?

Answer 1

First, some mock data:

x <- sample(LETTERS, 5, replace = TRUE)
y <- sample(LETTERS, 5, replace = TRUE)
z <- table(x, y)

Now here's a somewhat clumsy solution, using print.xtable's add.to.row argument.

comment          <- list()
comment$pos      <- list()
comment$pos[[1]] <- c(nrow(z))
comment$command  <- c(paste("\\hline \n",  # we`ll replace all default hlines with this and the ones below
                            "your footnote, caption or whatever.  \n",
                            sep = ""))
print(xtable(z),
      add.to.row = comment,
      hline.after = c(-1, 0))  # indicates rows that will contain hlines (the last one was defined up there)

If you want your comment to be placed before the data, use comment$pos[[1]] <- c(0) instead of comment$pos[[1]] <- c(nrow(z)) and adjust hline.after accordingly.

Here's my output:

% latex table generated in R 2.14.1 by xtable 1.7-0 package
% Mon Feb 20 02:17:58 2012
\begin{table}[ht]
\begin{center}
\begin{tabular}{rrrrr}
\hline
& B & C & P & V \\ 
\hline
A &   0 &   0 &   0 &   1 \\ 
D &   1 &   0 &   0 &   0 \\ 
I &   0 &   0 &   0 &   1 \\ 
P &   0 &   0 &   1 &   0 \\ 
Z &   0 &   1 &   0 &   0 \\ 
\hline
your footnote, caption or whatever.  
\end{tabular}
\end{center}
\end{table}

Answer 2

This is basically repurposing this answer, but this is the most programmatic way to do this with xtable. It's ugly, mainly because I hate the way xtable's add.to.row argument works.

Sample data:

set.seed(230)
DF <- data.frame(a = rnorm(5), b = rnorm(5), c = rnorm(5))

#of course, we can pass this directly below; I'm just saving
#  horizontal space for this answer
comm <- paste0("\\hline \n \\multicolumn{4}{l}",
           "{\\scriptsize{Check out these random numbers!}} \n")

print.xtable(xtable(DF, caption = "Describe the table"),
             #adjusting hline.after so that our comment appears
             #  "outside" the table, as defined by its border
             hline.after=c(-1, 0),
             #**NOTE: the first argument to add.to.row must be
             #  a list -- don't ask me why since it strikes me as odd**
             add.to.row = list(pos = list(5),
                               command = comm))

Here's the TeX output:

% latex table generated in R 3.2.4 by xtable 1.8-2 package
% Mon May 23 18:25:14 2016
\begin{table}[ht]
\centering
\begin{tabular}{rrrr}
  \hline
 & a & b & c \\ 
  \hline
1 & -0.23 & 0.04 & 1.34 \\ 
  2 & 0.10 & 0.57 & -1.62 \\ 
  3 & 0.33 & -0.14 & 0.83 \\ 
  4 & 0.36 & -0.75 & 0.20 \\ 
  5 & 0.44 & 0.13 & -0.49 \\ 
   \hline 
 \multicolumn{4}{l}{\scriptsize{Check out these random numbers!}} 
\end{tabular}
\caption{Describe the table} 
\end{table}

And the .pdf result if I wrap it with \documentclass{article}, \begin{document}, and \end{document}:

Of course, there are much more bells and whistles to add to get it publication-ready, but this is the crux and you should be well on your way.

Answer 3

If you are using RMarkdown, add this to the header:

---
(other configs here, like title, author, etc.)

header-includes:
    - \usepackage{caption}
    - \captionsetup{labelformat=empty}
---

Edit:

After talking with xtable package maintainer, David (that was very accessible), he came with this solution I post below:

I think this can be solved with xtableList. Create some data and convert the data frame to xtableList.

set.seed(230)
DF <- data.frame(a = rnorm(5), b = rnorm(5), c = rnorm(5))
library(xtable)
dfList <- list(DF)
attr(dfList, "message") <- c("A caption", "Which can have multiple lines")

Then xtable produces the following:

print(xtableList(dfList))
## % latex table generated in R 3.2.5 by xtable 1.8-3 package
## % Sat Jul 09 21:52:53 2016
## \begin{table}[ht]
## \centering
## \begin{tabular}{rrrr}
## \hline
## & a & b & c \\
## \hline
## 1 & -0.23 & 0.04 & 1.34 \\
## 2 & 0.10 & 0.57 & -1.62 \\
## 3 & 0.33 & -0.14 & 0.83 \\
## 4 & 0.36 & -0.75 & 0.20 \\
## 5 & 0.44 & 0.13 & -0.49 \\
## \hline
## \multicolumn{4}{l}{A caption}\\
##
## \multicolumn{4}{l}{Which can have multiple lines}\\
## \end{tabular}
## \end{table}

To deal with long captions you will need to split lines:

attr(dfList, "message") <- c("A caption", "Which can have", "multiple lines")