[R] Sweave, xtable plus/minus sign

[Ottorino-Luca Pantani]

Dear R-users,
please consider the following minimal example:

\documentclass[a4paper,titlepage,onecolumn,12pt]{article}
\usepackage[italian]{babel}
\usepackage{amssymb}
\usepackage[utf8x]{inputenc}
\usepackage[pdftex]{graphicx}
\begin{document}

<<label=test, echo=FALSE, results=tex>>=
df.data1 <-
  cbind.data.frame(A = rnorm(18),
                   B =factor(rep(LETTERS[1:6], each=3)))
myMean <- tapply(df.data1$A, df.data1$B, FUN = mean)
mySD <- tapply(df.data1$A, df.data1$B, FUN = sd)
foo <- matrix(c(myMean, mySD), ncol=2, nrow=6)
colnames(foo) <- c("Mean", "Std.Dev")
tmpTable <- xtable(foo, caption ="Simulated data",
     label="tab:four", digits=2)
print(tmpTable, caption.placement="top")
@

\end{document}

Is it possible to insert the plus/minus sign (±)  between the two columns ?
I mean within R/Sweave and not in the resulting .tex file ?

A possible workaround could be :
.......
foo.df <- as.data.frame(foo)
foo.df$Std.Dev <- paste("±", round(mySD,2), sep="")
tmpTable <- xtable(foo.df, caption ="Simulated data",
     label="tab:five", digits=2)
print(tmpTable, caption.placement="top")
@

Any other solution?
-- 
Ottorino-Luca Pantani, Università di Firenze
Dip.to di Scienze delle Produzioni Vegetali,
del Suolo e dell'Ambiente Forestale (DiPSA)
P.zle Cascine 28 50144 Firenze Italia
Ubuntu 10.04 -- GNU Emacs 23.1.50.1 (x86_64-pc-linux-gnu, GTK+ Version 
2.18.0)
ESS version 5.8 -- R 2.10.1