How to add elements to a plot using a knitr chunk without original markdown output?

Question

For documentary purposes, I want some code for a plot in the html-output, but not the plot. Later, I have to call the plotting code, and add something to the plot, but only seeing the additional code. I tried this: ```` ```{r non.finished.plotting, eval=FALSE} plot(1,type="n") ``` Some explanatory text here in the output: "This produces an empty plot, and we could now add some points to it manually." ```{r add.layer, fig.width=5, fig.height=5} <> points(x=rnorm(100,1,0.1), y=rnorm(100,0.8,0.1) ) ``` ```` I have found the echo-notation at Yihui's, but when I knit this, I get an error message in the output. ``` ## Error: plot.new has not been called yet ``` I also tried fiddling with the chunk options, but I could not find a combination which does what I want. (Sorry, this is very basic, but I did not find something quite like this example.)

Accepted Answer

Chunk references in `<<>>` do not respect chunk options, so `<>` will not work. What you can do is to move the chunk option `echo` back to the main chunk like this: ```` ```{r add.layer, fig.width=5, fig.height=5, echo=-1} <> points(x=rnorm(100,1,0.1), y=rnorm(100,0.8,0.1) ) ``` ```` `echo=-1` means do not echo the first expression (as documented). This is probably what you want:

How to add elements to a plot using a knitr chunk without original markdown output?

Solution

Problem