knitr - strange behaviour summary(numeric) prints different values than str() - knitr

Question

I am trying to develop a reproducible research report that includes printed output of the variable distributions of input datasets.
I am confused by the result of summary() in the small example below.
When I evaluate the code directly to the console I get 'b' is all 2012 as expected, however when I run this with knit2html() it appears as 2010.
dat <- data.frame(a = letters, b = rep(2012, length(letters)))
str(dat)
## 'data.frame': 26 obs. of 2 variables:
## $ a: Factor w/ 26 levels "a","b","c","d",..: 1 2 3 4 5 6 7 8 9 10 ...
## $ b: num 2012 2012 2012 2012 2012 ...
dd <- lapply(dat, summary)
dd
## $a
## a b c d e f g h i j k l m n o p q r s t u v w x y z
## 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
##
## $b
## Min. 1st Qu. Median Mean 3rd Qu. Max.
## 2010 2010 2010 2010 2010 2010
sessionInfo()
## R version 3.1.0 (2014-04-10)
## Platform: x86_64-pc-linux-gnu (64-bit)
##
## locale:
## [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=C
## [4] LC_COLLATE=C LC_MONETARY=C LC_MESSAGES=C
## [7] LC_PAPER=C LC_NAME=C LC_ADDRESS=C
## [10] LC_TELEPHONE=C LC_MEASUREMENT=C LC_IDENTIFICATION=C
##
## attached base packages:
## [1] stats graphics grDevices utils datasets methods base
##
## other attached packages:
## [1] knitr_1.5
##
## loaded via a namespace (and not attached):
## [1] evaluate_0.5.1 formatR_0.9 stringr_0.6.2 tools_3.1.0

Answer 1

In knitr code chunks, options("digits") defaults to 4. The summary function has a digits argument that defaults to max(3, getOption("digits")-3) (see ?summary). This causes summary to round 2012 to three significant digits, resulting in 2010.
You can either increase the digits option in your code chunk:
options(digits=7)
Or specify the digits argument in your call to summary:
dd <- lapply(dat, summary, digits=4)