# R-Markdown and Knitr Tutorial (Part 2)

In our last post we quickly went over how to create a new R-Markdown document and embed a Plotly graph in it. In this post we’ll get into more details around how to control code output using chunk options.

As shown in our previous post, for the embedded R code to be evaluated, it’ll need to be written inside a code-chunk as shown below.

### Chunk options

Knitr provides a lot of ways to control the output that shows up in the final document. We’ll highlight a few common ones.

#### Echo

echo allows control over visibility of the actual R code in a chunk. Set it to FALSE to hide the R code from showing up. Note that the code chunk will still be evaluated and any outputs mirrored in the final document. Use eval = FALSE if you do not need a code chunk to be evaluated at all.

### Message

Notice how if you use include() in a code chunk, messages from the R console are mirrored in the final document as well? By default, when knitr evaluates a code chunk, it mirrors any messages that show up in the console as well. We can turn that off using message = FALSE.

With message = TRUE

With message = FALSE

### Results

Controls the mirroring of output when a code chunk is evaluated. This includes text output as well as charts / graphs. Four values can be assigned: (see http://yihui.name/knitr/options/ for more details)

• markup – markup output using output hook
• asis – raw output
• hold – shows output after all code is evaluated
• hide – no output is shown

With results = ‘markup’

With results = ‘asis’

‘data.frame’: 32 obs. of 11 variables: $mpg : num 21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 …$ cyl : num 6 6 4 6 8 6 8 4 4 6 … $disp: num 160 160 108 258 360 …$ hp : num 110 110 93 110 175 105 245 62 95 123 … $drat: num 3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 …$ wt : num 2.62 2.88 2.32 3.21 3.44 … $qsec: num 16.5 17 18.6 19.4 17 …$ vs : num 0 0 1 1 0 1 0 1 1 1 … $am : num 1 1 1 0 0 0 0 0 0 0 …$ gear: num 4 4 4 3 3 3 3 4 4 4 … \$ carb: num 4 4 1 1 2 1 4 2 2 4 …

With results = ‘hide’