2.1 Matrices/data frames/tables

Matrices and data frames are printed as tables using the kable() function in knitr:

options(digits = 4)
set.seed(123)
x = matrix(rnorm(40), 5)
x

# with colunm names
dimnames(x) = list(NULL, head(LETTERS, ncol(x)))
x

# further customization via kable(), e.g. digits and captions
knitr::kable(x, digits = 2, caption = 'A table produced by printr.')

head(mtcars)

head(iris, 10)

For contingency tables, 1-d tables are printed as a 1-row matrix, 2-d tables are printed an \(n \times m\) matrix, and tables of higher dimensions are printed as data frames with frequencies.

x1 = sample(letters[1:3], 1000, TRUE)
x2 = sample(letters[1:3], 1000, TRUE)
x3 = sample(letters[1:3], 1000, TRUE)
table(x1)

table(x1, x2)

table(x1, x2, x3)

2.2 Search results from help.search()

Here are some examples demonstrating the results of help.search(), or you can also use ?? to search for a string.

??sunflower

help.search('contourplot')

help.search('foo', package = 'base')

help.search('foooooooo', package = 'utils')

## No results found

In a normal R session, the results will be displayed as an HTML page by default, but normally these functions are meant to be called in an interactive R session, and knitr documents are often compiled in non-interactive R sessions, so we changed the printing behavior of these results, and readers will get the basic idea of these functions when reading the knitr output. If they want to run these functions by themselves, they can do it in an interactive R session.

2.3 Help pages

When you want to read the help page of a certain R object, you normally use ? or help(), which will launch a separate help page from the R session, and require human interaction. Again, we may not desire human interactions in knitr documents, so the help pages are printed as static documents here.

?coef

coef(object, ...)
coefficients(object, ...)
## Default S3 method:
coef(object, complete = TRUE, ...)
## S3 method for class 'aov'
coef(object, complete = FALSE, ...)

x <- 1:5; coef(lm(c(1:3, 7, 6) ~ x))

When help pages are really long, we can use the chunk option printr.help.sections to select a few sections to display, e.g. we only show the sections description and usage of the paste() function:

?paste

paste (..., sep = " ", collapse = NULL, recycle0 = FALSE)
paste0(...,            collapse = NULL, recycle0 = FALSE)

2.4 Vignette/dataset lists

We can print the lists of vignettes and datasets in packages using vignette() and data(), respectively.

vignette(package = 'rpart')

vignette(package = c('rpart', 'knitr'))

data(package = 'lattice')

data(package = c('rpart', 'lattice'))

data(package = 'knitr')  # no datasets here

## Data sets not found

browseVignettes(package = 'knitr')

## No vignettes found

2.5 Package info

A description of a package can be printed via library(help = 'foo'):

library(help = 'printr')

        Information on package 'printr'

Description:

Package:           printr
Type:              Package
Title:             Automatically Print R Objects to Appropriate Formats According to the
                   'knitr' Output Format
Version:           0.2
Author:            Yihui Xie
Maintainer:        Yihui Xie <xie@yihui.name>
Description:       Extends the S3 generic function knit_print() in 'knitr' to
                   automatically print some objects using an appropriate format such as
                   Markdown or LaTeX. For example, data frames are automatically printed
                   as tables, and the help() pages can also be rendered in 'knitr'
                   documents.
Imports:           knitr (>= 1.31)
Suggests:          tools, rmarkdown
License:           GPL
URL:               https://yihui.org/printr/
BugReports:        https://github.com/yihui/printr/issues
VignetteBuilder:   knitr
RoxygenNote:       7.1.1
Encoding:          UTF-8
Built:             R 4.1.1; ; 2021-09-27 19:39:24 UTC; unix

Index:

printr                  Print R objects in 'knitr' documents nicely