R / Sweave formatting numbers with \Sexpr{} in scientific notation

Question

I am just starting to write some documents with Sweave/R and I like the \\sexpr{} command that lets one tow write numbers directly within text.

Answer 1

An example using siunitx link to pdf. In the preamble you can define your default options which you may override later in the document.

For numeric output :

num <- function(x,round_precision=NULL)
{
  if (is.null(round_precision)) {
    return(sprintf("\\num{%s}", x))
  } else {
    return(sprintf("\\num[round-precision=%s]{%s}",round_precision, x))
  }
}

For scientific output :

sci<- function(x,round_precision=NULL){
  if (is.null(round_precision)) {
  return(sprintf("\\num[scientific-notation = true]{%s}", x))
} else {
  return(sprintf("\\num[round-precision=%s,scientific-notation = true]{%s}",round_precision, x))
}
}

Here is a full reproducible .Rnw script (to be used with knitr ... for sweave use four antislashes in the functions instead of two see this SO post.)

\documentclass[a4paper]{article}
\usepackage{siunitx}
%\usepackage{Sweave}
\title{siunitx}

\sisetup{
round-mode = figures,
round-precision = 3,
group-separator = \text{~}
}
\begin{document}

\maketitle
<>=
num <- function(x,round_precision=NULL)
{
  if (is.null(round_precision)) {
    return(sprintf("\\num{%s}", x))
  } else {
    return(sprintf("\\num[round-precision=%s]{%s}",round_precision, x))
  }
}

sci<- function(x,round_precision=NULL){
  if (is.null(round_precision)) {
  return(sprintf("\\num[scientific-notation = true]{%s}", x))
} else {
  return(sprintf("\\num[round-precision=%s,scientific-notation = true]{%s}",round_precision, x))
}
}

@
Examples :\\
$num$ for number formatting :

\begin{itemize}
\item \textbf{num(pi, round\_precision=2)} $\Rightarrow$
\num[round-precision=2]{3.14159265358979} 
\item \textbf{num(pi, round\_precision=4)}  $\Rightarrow$
\num[round-precision=4]{3.14159265358979}
\item The default formatting (here round-precision=3) is taken from
\textbf{\textbackslash sisetup} 
\textbf{num(pi)}  $\Rightarrow$ \num{3.14159265358979}\\
\end{itemize}

\noindent $sci$ for scientific notation :

\begin{itemize}
\item \textbf{sci(12.5687e4)}  $\Rightarrow$ \num[scientific-notation =
true]{125687}
\item \textbf{sci(125687.11111)}  $\Rightarrow$
\num[scientific-notation = true]{125687.11111}
\item \textbf{sci(125687.11111, round\_precision=4)} $\Rightarrow$
 \Sexpr{sci(125687.11111, round_precision=4)}
\end{itemize}

\end{document}