How to put square brackets on elements in specific rows of a matrix in R

Question

I want to export my outputs from R to latex using xtable. In addition, I want each of the tables to have an estimate and its standard error. How do I get the elements of a particular row of the matrix in box brackets in R?

The expected output by applying function xtable to the resulting data frame should be as follows:

 \begin{tabular}{lcccc}
 \hline
 & Hi & MV & Zi & Pi \\ 
 \hline
 Mean & 0.57 & 0.50 & 0.54 & 0.42  \\ 
 & [0.01] & [0.01] & [0.01] & [0.05]  \\ 
 Median & 0.57 & 0.50 & 0.54 & 0.42  \\ 
 & [0.01] & [0.01] & [0.01] & [0.05]  \\ 
 MSE & 0.08 & 0.02 & 0.05 & 0.16  \\ 
 & [0.01] & [0.00] & [0.01] &[ 0.04]  \\ 
\hline
\end{tabular}

Thank you.

Answer 1

you could try this,

x<-matrix(1:12,nrow=4)

bracket <- function(x, i, j){
  x[i,j] <- sprintf("[%s]", x[i,j])
  x
}

# x <- bracket(x, 2, 3) # test

# every second row
ind = which(row(x) %% 2 == 1, arr.ind = TRUE)
x <- bracket(x, ind[,1], ind[,2])

print(xtable(x), sanitize.text.function = I)

Note: I would probably define a LaTeX macro, e.g. \newcommand{\wrap}[1]{\ensuremath{\left[#1\right]}}, with x[i,j] <- sprintf("\\wrap{%s}", x[i,j]) in the R code.

Answer 2

I found this works for my case but then may be some one can come up with a more efficient way. Suppose, I want to put square brackets on elements in the odd rows, then this miniature program works:

 x<-matrix(1:12,4,byrow=TRUE)
y<-matrix(NA,ncol=ncol(x),nrow=nrow(x))
Y<-t(sapply(1:nrow(x),function(i){
if(i%%2!=0){y[i,]<-x[i,]
  }else{
  y[i,]<-paste0("[",x[i,],"]")
  }
 }))

print(xtable(Y))