Search code examples
rpdferror-handlingknitrsweave

Customize error message when compiling PDF

Given the following R knitr document:

\documentclass{article}
\begin{document}

<<data>>=
opts_chunk$set(comment = NA)  # omits "##" at beginning of error message
x <- data.frame(x1 = 1:10)
y <- data.frame()
@ 

<<output_x>>=
if (nrow(x) == 0) stop("x is an empty data frame.") else summary(x)
@

<<output_y>>=
if (nrow(y) == 0) stop("y is an empty data frame.") else summary(y)
@

\end{document}

As expected, the last chunk returns an error with the custom message. The compiled PDF looks a little different:

Error: y is an empty data frame.

I want this text to just be

y is an empty data frame.

Without the Error: part or the red color. Can I achieve this? How?

Edit: I was able to make it in the mock data through the following workaround:

<<output_y>>=
if (nrow(y) == 0) cat("y is an empty data frame.") else summary(y)
@

However, that doesn't work with my real data, because I need the function to be stopped at that point.

Solution

  • Although I do not understand why an error should not be called Error, you are free to customize the output hook error to remove Error: from the message:

    library(knitr)
knit_hooks$set(error = function(x, options) {
  knitr:::escape_latex(sub('^Error: ', '', x))
})