Concatenate text with knitr

Question

Using knitr, I want to print the results of several functions for some variable, e.g.

There were x1 (a=\`r a(x1)\`; b=\`r b(x1)\`) and x2 (a=\`r a(x2)\`; b=\`r b(x2)\`)

Since I don't like to repeat this for every variable, I wrote a function to generate the string:

foo <- function(x) paste('a = ',a(x), '; b = ', b(x))

Now I can write There were x1 (`r foo(x1)`) and x2 (`r foo(x2)`).

It works, but doesn't use options('digits'), so it prints 15 digits. cat() uses options('digits'), but apprently using cat is discouraged and doesn't output anything when using inline code.

Is there an alternative to paste() that formats numbers with `options('digits') and creates output in inline chunks?

Answer 1

"Using of cat discouraged": this is a misunderstanding. Yihui warns against using cat to output messages. If you want to created clean output, you often must use cat. Try the following in your chunk:

options(digits=2)
x1 = 2.304302
# chunk output
x1 # Ugly, [1]
cat(x1,"\n") # Must use cat here, to avoid the [1] printed

Re you main question: No chance here without explicit formating in your foo function, probably best with sprintf. Options only applies in the inline numeric code, not to strings as supplied by your function foo. knitr does not interfere with the function of paste, and paste does not honor options.

x2 = 4.489324802    
options(digits=2)
paste(x2)

"4.489324802"

Answer 2

Probably format(x, ...) would work for this. (not tested)