comments splitting into multiple lines in RMarkdown - r-markdown

Question

I'm writing a document in RMarkdown, and sometimes I want to have comments in my code chunks that show in the PDF, like this:
vector <- 1:4
# finds the mean of these values
mean(vector)
## [1] 2.5
However, when I knit the PDF (or HTML document), it breaks the comment up into one-word lines, like this:
vector <- 1:4
# finds
# the
# mean
# of
# these
# values
mean(vector)
## [1] 2.5
This is really annoying, and it makes my documents way longer than they need to be. How can I fix it?
EDIT: updated all packages; here's the session info:
> sessionInfo()
R version 3.3.1 (2016-06-21)
Platform: i386-w64-mingw32/i386 (32-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1
locale:
[1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United States.1252 LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C LC_TIME=English_United States.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] abind_1.4-5
loaded via a namespace (and not attached):
[1] backports_1.0.5 magrittr_1.5 rprojroot_1.2 htmltools_0.3.5 tools_3.3.1 yaml_2.1.14 Rcpp_0.12.9 stringi_1.1.2
[9] rmarkdown_1.3 knitr_1.15.1 stringr_1.1.0 digest_0.6.12 evaluate_0.10

Answer 1

It might be caused by knitr/formattR's code tidying, with a width.cutoff set too small. You can check your chunk options with:
opts_chunk$get()
And maybe set a larger width.cutoff; formatR will try to make sure no line in your code has a higher number of character than this:
opts_chunk$set(tidy=T‌​RUE,
tidy.opts=list(width.cutoff=60))