An Introduction to the printr Package

Yihui Xie

2026-01-16

The printr (read “printer” or “print R”) package is a companion package to knitr. Its main purpose is to extend the S3 generic function knit_print() in knitr, which is the default value of the chunk option render, as explained in the vignette knit_print.html.

Overview

To enable the printing methods defined in this package, just library(printr) or loadNamespace('printr') in a code chunk (in the beginning) of your knitr document. Then some objects will be printed differently with what you would have seen in a normal R console. For example:

• matrices, data frames, and contingency tables are printed as tables (LaTeX, HTML, or Markdown, depending on your output format)
• the help page (from ?foo or help(foo)) can be rendered as HTML, LaTeX, or plain text, and you can also specify which section(s) of the help page to include in the output
• the results from browseVignettes(), help.search(), data(), and vignette() are rendered as tables
• the package information from library(help = 'foo') is rendered as plain text

To disable the printing methods in this package, you can call detach('package:printr', unload = TRUE) if you attached the package via library(printr) before, or unloadNamespace('printr') if you loaded it via loadNamespace('printr').

This package aims to be portable in the sense that it should work in most document formats, including *.Rnw (R + LaTeX), *.Rmd (R Markdown), and *.Rhtml (R + HTML) files, etc.

You can find the package source as well as installation instructions on Github, and you are welcome to contribute code via pull requests, or file feature requests and bug reports via Github issues.

Examples

First we take a look at a quick example of printing some R objects in the R console:

> # R uses plain text representation for data frames/matrices/...
> head(mtcars)

                   mpg cyl disp  hp drat    wt  qsec vs am gear carb
Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1

> head(iris)

  Sepal.Length Sepal.Width Petal.Length Petal.Width Species
1          5.1         3.5          1.4         0.2  setosa
2          4.9         3.0          1.4         0.2  setosa
3          4.7         3.2          1.3         0.2  setosa
4          4.6         3.1          1.5         0.2  setosa
5          5.0         3.6          1.4         0.2  setosa
6          5.4         3.9          1.7         0.4  setosa

Then we attach the printr package in this R session, and see how things change later:

library(printr)

## Registered S3 method overwritten by 'printr':
##   method                from     
##   knit_print.data.frame rmarkdown

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

-0.5605	1.7151	1.2241	1.7869	-1.0678	-1.6867	0.4265	0.6886
-0.2302	0.4609	0.3598	0.4979	-0.2180	0.8378	-0.2951	0.5539
1.5587	-1.2651	0.4008	-1.9666	-1.0260	0.1534	0.8951	-0.0619
0.0705	-0.6869	0.1107	0.7014	-0.7289	-1.1381	0.8781	-0.3060
0.1293	-0.4457	-0.5558	-0.4728	-0.6250	1.2538	0.8216	-0.3805

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

A	B	C	D	E	F	G	H
-0.5605	1.7151	1.2241	1.7869	-1.0678	-1.6867	0.4265	0.6886
-0.2302	0.4609	0.3598	0.4979	-0.2180	0.8378	-0.2951	0.5539
1.5587	-1.2651	0.4008	-1.9666	-1.0260	0.1534	0.8951	-0.0619
0.0705	-0.6869	0.1107	0.7014	-0.7289	-1.1381	0.8781	-0.3060
0.1293	-0.4457	-0.5558	-0.4728	-0.6250	1.2538	0.8216	-0.3805

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

A table produced by printr.

A	B	C	D	E	F	G	H
-0.56	1.72	1.22	1.79	-1.07	-1.69	0.43	0.69
-0.23	0.46	0.36	0.50	-0.22	0.84	-0.30	0.55
1.56	-1.27	0.40	-1.97	-1.03	0.15	0.90	-0.06
0.07	-0.69	0.11	0.70	-0.73	-1.14	0.88	-0.31
0.13	-0.45	-0.56	-0.47	-0.63	1.25	0.82	-0.38

head(mtcars)

	mpg	cyl	disp	hp	drat	wt	qsec	vs	am	gear	carb
Mazda RX4	21.0	6	160	110	3.90	2.620	16.46	0	1	4	4
Mazda RX4 Wag	21.0	6	160	110	3.90	2.875	17.02	0	1	4	4
Datsun 710	22.8	4	108	93	3.85	2.320	18.61	1	1	4	1
Hornet 4 Drive	21.4	6	258	110	3.08	3.215	19.44	1	0	3	1
Hornet Sportabout	18.7	8	360	175	3.15	3.440	17.02	0	0	3	2
Valiant	18.1	6	225	105	2.76	3.460	20.22	1	0	3	1

head(iris, 10)

Sepal.Length	Sepal.Width	Petal.Length	Petal.Width	Species
5.1	3.5	1.4	0.2	setosa
4.9	3.0	1.4	0.2	setosa
4.7	3.2	1.3	0.2	setosa
4.6	3.1	1.5	0.2	setosa
5.0	3.6	1.4	0.2	setosa
5.4	3.9	1.7	0.4	setosa
4.6	3.4	1.4	0.3	setosa
5.0	3.4	1.5	0.2	setosa
4.4	2.9	1.4	0.2	setosa
4.9	3.1	1.5	0.1	setosa

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)

a	b	c
320	331	349

table(x1, x2)

x1/x2	a	b	c
a	103	109	108
b	108	115	108
c	123	103	123

table(x1, x2, x3)

x1	x2	x3	Freq
a	a	a	41
		b	26
		c	36
	b	a	34
		b	31
		c	44
	c	a	34
		b	33
		c	41
b	a	a	37
		b	36
		c	35
	b	a	40
		b	31
		c	44
	c	a	36
		b	38
		c	34
c	a	a	31
		b	46
		c	46
	b	a	25
		b	35
		c	43
	c	a	46
		b	46
		c	31

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

Package	Topic	Title
graphics	sunflowerplot	Produce a Sunflower Scatter Plot
grDevices	xyTable	Multiplicities of (x,y) Points, e.g., for a Sunflower Plot

help.search('contourplot')

Package	Topic	Title
graphics	filled.contour	Level (Contour) Plots
lattice	levelplot	Level plots and contour plots
lattice	panel.levelplot	Panel Functions for levelplot and contourplot

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

Package	Topic	Title
base	is.things	Explore some properties of R objects and is.FOO() functions. Not for newbies!

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.

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	R Documentation

Extract Model Coefficients

Description

coef is a generic function which extracts model coefficients from objects returned by modeling functions. coefficients is an alias for it.

Usage

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

Arguments

object	an object for which the extraction of model coefficients is meaningful.
complete	for the default (used for lm, etc) and aov methods: logical indicating if the full coefficient vector should be returned also in case of an over-determined system where some coefficients will be set to NA, see also alias. Note that the default differs for lm() and aov() results.
...	other arguments.

Details

All object classes which are returned by model fitting functions should provide a coef method or use the default one. (Note that the method is for coef and not coefficients.)

The "aov" method does not report aliased coefficients (see alias) by default where complete = FALSE.

The complete argument also exists for compatibility with vcov methods, and coef and aov methods for other classes should typically also keep the complete = * behavior in sync. By that, with p <- length(coef(obj, complete = TF)), dim(vcov(obj, complete = TF)) == c(p,p) will be fulfilled for both complete settings and the default.

Value

Coefficients extracted from the model object object.

For standard model fitting classes this will be a named numeric vector. For "maov" objects (produced by aov) it will be a matrix.

References

Chambers, J. M. and Hastie, T. J. (1992) Statistical Models in S. Wadsworth & Brooks/Cole.

See Also

fitted.values and residuals for related methods; glm, lm for model fitting.

Examples

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

R Documentation

Concatenate Strings

Description

Concatenate vectors after converting to character. Concatenation happens in two basically different ways, determined by collapse being a string or not.

Usage

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

Vignette/dataset lists

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

vignette(package = 'rpart')

Vignettes in rpart

Item	Title
longintro	Introduction to Rpart (source, pdf)
usercode	User Written Split Functions (source, pdf)

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

Vignettes

Package	Item	Title
rpart	longintro	Introduction to Rpart (source, pdf)
rpart	usercode	User Written Split Functions (source, pdf)
knitr	knitr-html	An R HTML Vignette with knitr (source, html)
knitr	knitr-markdown	An R Markdown Vignette with knitr (source, html)
knitr	knit_print	Custom Print Methods (source, html)
knitr	datatables	Display Tables with the JavaScript Library DataTables (source, html)
knitr	knitr-refcard	knitr Reference Card (source, pdf)
knitr	knitr-intro	Not an Introduction to knitr (source, html)
knitr	docco-classic	R Markdown with the Docco Classic Style (source, html)
knitr	docco-linear	R Markdown with the Docco Linear Style (source, html)
knitr	knit_expand	Templating with knit_expand() (source, html)

data(package = 'lattice')

Data sets in lattice

Item	Title
USMortality	Mortality Rates in US by Cause and Gender
USRegionalMortality	Mortality Rates in US by Cause and Gender
barley	Yield data from a Minnesota barley trial
environmental	Atmospheric environmental conditions in New York City
ethanol	Engine exhaust fumes from burning ethanol
melanoma	Melanoma skin cancer incidence
singer	Heights of New York Choral Society singers

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

Data sets

Package	Item	Title
rpart	car.test.frame	Automobile Data from ‘Consumer Reports’ 1990
rpart	car90	Automobile Data from ‘Consumer Reports’ 1990
rpart	cu.summary	Automobile Data from ‘Consumer Reports’ 1990
rpart	kyphosis	Data on Children who have had Corrective Spinal Surgery
rpart	solder	Soldering of Components on Printed-Circuit Boards
rpart	solder.balance (solder)	Soldering of Components on Printed-Circuit Boards
rpart	stagec	Stage C Prostate Cancer
lattice	USMortality	Mortality Rates in US by Cause and Gender
lattice	USRegionalMortality	Mortality Rates in US by Cause and Gender
lattice	barley	Yield data from a Minnesota barley trial
lattice	environmental	Atmospheric environmental conditions in New York City
lattice	ethanol	Engine exhaust fumes from burning ethanol
lattice	melanoma	Melanoma skin cancer incidence
lattice	singer	Heights of New York Choral Society singers

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

## Data sets not found

browseVignettes(package = 'knitr')

Vignette	Title
knitr-html.html	An R HTML Vignette with knitr
knitr-markdown.html	An R Markdown Vignette with knitr
knit_print.html	Custom Print Methods
datatables.html	Display Tables with the JavaScript Library DataTables
knitr-refcard.pdf	knitr Reference Card
knitr-intro.html	Not an Introduction to knitr
docco-classic.html	R Markdown with the Docco Classic Style
docco-linear.html	R Markdown with the Docco Linear Style
knit_expand.html	Templating with knit_expand()

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:            0.3.1
Authors@R:          c( person("Yihui", "Xie", role = c("aut", "cre"), email =
                    "xie@yihui.name", comment = c(ORCID = "0000-0003-0645-5666")) )
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:        7.2.3
Encoding:           UTF-8
NeedsCompilation:   no
Packaged:           2026-01-16 21:58:55 UTC; rforge
Author:             Yihui Xie [aut, cre] (ORCID: <https://orcid.org/0000-0003-0645-5666>)
Maintainer:         Yihui Xie <xie@yihui.name>
Built:              R 4.5.0; ; 2026-01-16 21:58:56 UTC; unix

Index:

printr                  Print R objects in 'knitr' documents nicely