No increment of a variable in a Sweave code chunk which is wrapped by a \whiledo loop

Question

I already searched in different forums but until now I couldn’t find a solution. So I hope that you can help me…

Like mentioned in the title there is no increment of my variable x in the code chunk which is wrapped by a \whiledo loop. Let’s have a look at my code:

    \documentclass[10pt, a4paper]{article}
    \usepackage{ifthen}
    \usepackage{pifont}

    \begin{document}
    \SweaveOpts{concordance=TRUE}

    \newcounter{ctra}
    \setcounter{ctra}{1}
    \whiledo {\value{ctra} < 7}
    {

         <<echo=FALSE, results=hide>>=

         if(!exists("x")){x=numeric()}

         if(length(x)==0)
         {
         x=2
         }else{
         x=x+1
         }
         @

    \Sexpr{x} \\
    \stepcounter{ctra}
    }
    \end{document}

When I now compile the script in RStudio I get a pdf with a bunch of 2 but I expected a numerical series like 2, 3, 4, 5, 6 and 7.

Can anybody give me a hint to solve that problem? And please explain the background if necessary, because I’m not very experienced in Sweave.

Here I edit my question for the first time…

This numerical series I need to get the right data into my table. The code of two table rows will be something like that

    \setlength{\arrayrulewidth}{1pt}
    \begin{tabular}{|p{3.5cm}*{5}{p{1.75cm}}|}
    \hline
    \textbf{Stab} & \textbf{\ctab Spr \Sexpr{vers[1]}} & \textbf{\ctab Spr \Sexpr{vers[2]}} & \textbf{\ctab Spr \Sexpr{vers[3]}} & \textbf{\ctab Spr \Sexpr{vers[4]}} & \textbf{\ctab Spr \Sexpr{vers[5]}} \\
    \hline
    \rowcolor[gray]{0.7} 
    \hspace{0.5cm}Dampf [-] & \ctab \Sexpr{Drsp[[1]][vers[1]]} & \ctab \Sexpr{Drsp[[1]][vers[2]]} & \ctab \Sexpr{Drsp[[1]][vers[3]]} & \ctab \Sexpr{Drsp[[1]][vers[4]]} & \ctab    \Sexpr{Drsp[[1]][vers[5]]} \\
    \hspace{0.5cm}MaUbschw [bar] & \ctab \Sexpr{Drsp[[2]][ vers[1]]} & \ctab \Sexpr{Drsp[[2]][vers[2]]} & \ctab \Sexpr{Drsp[[2]][vers[3]]} & \ctab \Sexpr{Drsp[[2]][vers[4]]} & \ctab \Sexpr{Drsp[[2]][vers[5]]} \\
    % and so on...
    \hline
    \end{tabular}

But my above loaded data – in the script - has a high quantity of rows – up to 200 rows. The data file is comparable with an R data.frame.

One row in my data will be one column in my table.

This is too much to put it just in one table. My solution is to put a loop over the table and create a table with only 5 columns. In the pdf I will have some tables one below the other.

Therefore I make a vector with the quantity of rows.

    vers=c(1:nrow(Drsp)) # R-code

In the first loop the first elements of the vector will be taken to fill the table with 5 columns. Because I have 5 columns I can “shorten” the vector before we will go in the second loop.

    vers=vers[-c(1:5)] # R-code

For the second table I have the right data in the first 5 elements of the vector.

I think now it’s time to have a look at my compound code:

    \documentclass[10pt, a4paper]{article}
    \usepackage{ifthen}
    \usepackage{pifont}

    % Centering in the table
    \newcommand{\ctab}{\centering\arraybackslash}

    \begin{document}
    \SweaveOpts{concordance=TRUE}

    <<echo=FALSE, results=hide>>=

    # Load the required data
    Drsp=read.csv2(file="F:\\Testfile.csv”,header=TRUE)  

    # Create the vector
    vers=c(1:nrow(Drsp))
    @


    \newcounter{ctra}
    \setcounter{ctra}{1}
    \whiledo {\value{ctra} < \Sexpr{nrow(Drsp)}}
    {

    <<echo=FALSE, results=hide>>=

    if(!exists("x")){x=numeric()}

    if(x>=1){vers=vers[-c(1:5)]} # shorten my vector in every loop

    if(length(x)==0)
    {
      x=1
    }else{
      x=x+1
    }
    @


    % table with the right data, because every loop the vector will be shorten
    \setlength{\arrayrulewidth}{1pt}
    \begin{tabular}{|p{3.5cm}*{5}{p{1.75cm}}|}
    \hline
    \textbf{Stab} & \textbf{\ctab Spr \Sexpr{vers[1]}} & \textbf{\ctab Spr \Sexpr{vers[2]}} & \textbf{\ctab Spr \Sexpr{vers[3]}} & \textbf{\ctab Spr \Sexpr{vers[4]}} & \textbf{\ctab Spr \Sexpr{vers[5]}} \\
    \hline
    \rowcolor[gray]{0.7} 
    \hspace{0.5cm}Dampf [-] & \ctab \Sexpr{Drsp[[1]][vers[1]]} & \ctab \Sexpr{Drsp[[1]][ vers[2]]} & \ctab \Sexpr{Drsp[[1]][ vers[3]]} & \ctab \Sexpr{Drsp[[1]][ vers[4]]} & \ctab    \Sexpr{Drsp[[1]][ vers[5]]} \\
    \hspace{0.5cm}MaUbschw [bar] & \ctab \Sexpr{Drsp[[2]][ vers[1]]} & \ctab \Sexpr{Drsp[[2]][ vers[2]]} & \ctab \Sexpr{Drsp[[2]][ vers[3]]} & \ctab \Sexpr{Drsp[[2]][ vers[4]]} & \ctab \Sexpr{Drsp[[2]][ vers[5]]} \\
    % and so on...         
    \hline
    \end{tabular}

    \addtocounter{ctra}{5}  % because of the 5 table columns


    }  % End whiledo loop
    \end{document}

Okay, I hope I have done everything right…

If there is a easier way to reach my goal please let me know;-)

Many thanks in advance!

Answer 1

Sweave processes the source file by ignoring all LaTeX code and executing the R code. This means that code in a LaTeX loop will be executed only once by R. In the generated .tex code any \Sexpr variables are substituted by the value after the single run, in this case \Sexpr{x} is replaced by the string 2. When running LaTeX afterwards, the loop is executed and the string 2 is printed several times.

As an alternative you can put the loop in R and write the desired LaTeX code from there. MWE (save as .Snw, run from within R Sweave("yourfile.Snw"), then compile the generated yourfile.tex):

Edit: new Snw file, same idea, a bit more complex code

Adjust to taste. Convert \ into \\ and put a \n where you want a newline.

\documentclass{article}
\begin{document}
<<results=tex,echo=FALSE>>=

lines_per_table <- 5
cols_per_table <- 4

Drsp <- matrix(rexp(100, rate=.1), ncol=20)
vers <- c(1:ncol(Drsp))

for(x in seq(0,ncol(Drsp),lines_per_table)){
   cat("\\begin{tabular}{l|ccccc|}\n")
   cat("\\hline\n")
   cat("\\textbf{Stab} ")
   for(y in seq(cols_per_table)){
      cat("& Spr",vers[y])
   }
   cat("\\\\\n")
   cat("\\hline\n")
   for(y in seq(lines_per_table)){
      cat("line",y)
      for(z in seq(cols_per_table)){
      cat("&",Drsp[y,vers[z]])
   }
   cat("\\\\\n")
   }
   cat("\\hline\n")
   cat("\\end{tabular}\n\n")
   vers <- vers[-c(1:cols_per_table)]  
}
@
\end{document}

Result:

etc.

End edit

yourfile.Snw

\documentclass{article}
\begin{document}
\noindent
<<results=tex,echo=FALSE>>=
for(x in seq(7)){
   cat("x is \\textbf{",x,"}\\\\",sep="")
}
@
\end{document}

Mind the results=tex option.

Auto-generated yourfile.tex

\documentclass{article}
\usepackage{Sweave}
\begin{document}
\noindent
x is \textbf{1}\\x is \textbf{2}\\x is \textbf{3}\\x is \textbf{4}\\x is \textbf{5}\\x is \textbf{6}\\x is \textbf{7}\\\end{document}

Result:

x is 1

x is 2

x is 3

x is 4

x is 5

x is 6

x is 7