flextable overview

Introduction

flextable can easily create reporting table from data.frame. You can merge cells, add header rows, add footer rows, change any format and specify how data should be displayed in cells. Tables content can also contain mixed type of content, text and images.

flextable objects can be rendered in HTML format, Microsoft Word, Microsoft PowerPoint and PDF.

The following table is made with function flextable and dataset data:

data <- iris[c(1:3, 51:53, 101:104),]
data
#>     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
#> 51           7.0         3.2          4.7         1.4 versicolor
#> 52           6.4         3.2          4.5         1.5 versicolor
#> 53           6.9         3.1          4.9         1.5 versicolor
#> 101          6.3         3.3          6.0         2.5  virginica
#> 102          5.8         2.7          5.1         1.9  virginica
#> 103          7.1         3.0          5.9         2.1  virginica
#> 104          6.3         2.9          5.6         1.8  virginica

Species		Sepal		Petal
setosa		5.1	3.5		1.4	0.2
	4.9	3.0		1.4	0.2
	4.7	3.2		1.3	0.2
versicolor		7.0	3.2		4.7	1.4
	6.4	3.2		4.5	1.5
	6.9	3.1		4.9	1.5
virginica		6.3	3.3		6.0	2.5
	5.8	2.7		5.1	1.9
	7.1	3.0		5.9	2.1
	6.3	2.9		5.6	1.8

Getting started

The main function is flextable.

flextable function is producing flexible tables where each cell can contain several chunks of text with their own set of formatting properties (bold, font color, etc.).

The function is using default values to format the table. It is also using a simple formatting function to create the paragraphs of text that will be rendered in each cell. All these default values can be modified after the flextable creation.

The following illustration is presenting most of the functions available to format a flextable:

Let’s have a step by step demo. First create a flextable and change header font in bold.

library(flextable)
library(officer)

myft <- flextable(
  head(mtcars), 
  col_keys = c("am", "carb", "gear", "mpg", "drat" ))
myft

am	carb	gear	mpg	drat
1	4	4	21	3.9
1	4	4	21	3.9
1	1	4	23	3.9
0	1	3	21	3.1
0	2	3	19	3.1
0	1	3	18	2.8

flextable: it is creating a flextable object based on input data. Optional argument col_keys is used to only display a subset of columns.

Functions theme_ are sugar functions whose role is to apply a set of formatting instructions to a flextable. For example, theme_vanilla set specific borders, right align paragraphs and make headers bold.

myft <- theme_vanilla(myft)
myft

am	carb	gear	mpg	drat
1	4	4	21	3.9
1	4	4	21	3.9
1	1	4	23	3.9
0	1	3	21	3.1
0	2	3	19	3.1
0	1	3	18	2.8

Layout

Table layout can be modified. One can add or change header/footer rows, change cells height and width and merge cells.

Also, there is an important function named autofit (it adjusts widths and heights regarding to text widths and heights).

myft <- merge_v(myft, j = c("am", "carb") )
myft <- set_header_labels( myft, carb = "# carb." )
myft <- autofit(myft)
myft <- theme_vader(myft)
myft

am	# carb.	gear	mpg	drat
1	4	4	21	3.9
4	21	3.9
1	4	23	3.9
0	3	21	3.1
2	3	19	3.1
1	3	18	2.8

To learn more, see article about layouts.

Formatting

To learn more, see article about format.

Many sugar functions can be used to format flextables: bg(), fontsize(), italic(), bold(), color(), padding()…

Conditional formatting can be made by using the selector arguments. All formatting functions are accepting selector arguments.

myft <- theme_vanilla(myft)
myft <- color(myft, color = "black", part = "all")
myft <- bg(myft, bg = "transparent", part = "all")
myft <- italic(myft, j = 1)
myft <- bg(myft, bg = "#C90000", part = "header")
myft <- color(myft, color = "white", part = "header")
myft <- color(myft, ~ drat > 3.5, ~ drat, color = "red")
myft <- bold(myft, ~ drat > 3.5, ~ drat, bold = TRUE)
myft <- autofit(myft)
myft

am	# carb.	gear	mpg	drat
1	4	4	21	3.9
4	21	3.9
1	4	23	3.9
0	3	21	3.1
2	3	19	3.1
1	3	18	2.8

Keypoints

A flextable is an object that will produce a reporting table from a data.frame object.
A flextable is containing three parts, header, body and footer. By default, there is only one header row containing the names of the data.frame. The body part is containing data from the data.frame. The footer part is not implemented by default.
Any formatting property related to text, paragraphs, cells in the table can be modified. Lot of default values are available with function get_flextable_defaults() and can be updated with function set_flextable_defaults().
A cell is made of one single paragraph of text. Paragraphs can contain several chunks of text with different formatting but also images.
The dimensions of the flextable elements, widths of columns and heights of rows, are always defined. Being able to define the exact size necessary to display data on a single line is a choice made to make sure HTML, pptx, docx, images have all the same rendering, for that exact widths and heights were needed. In most of cases, you should not worry about that by only using autofit() as last operation. See functions autofit() and dim_pretty().
Columns to display (col_keys) are by default all columns of the data.frame but can be choosen from a subset of existing columns and also non-existent columns. Non-existent columns contain blanks by default but this content can be customized.

Flextable rendering

When working in RStudio, flextable will be printed in the rstudio viewer pane, the default format is HTML output.

We will use the following example:

ft <- flextable(head(mtcars))
ft <- autofit(ft)
ft

mpg	cyl	disp	hp	drat	wt	qsec	vs	am	gear	carb
21	6	160	110	3.9	2.6	16	0	1	4	4
21	6	160	110	3.9	2.9	17	0	1	4	4
23	4	108	93	3.9	2.3	19	1	1	4	1
21	6	258	110	3.1	3.2	19	1	0	3	1
19	8	360	175	3.1	3.4	17	0	0	3	2
18	6	225	105	2.8	3.5	20	1	0	3	1

R Markdown documents

One great feature of flextables is that it can be used in R Markdown documents; HTML, Word, PowerPoint and PDF outputs are managed with method knitr::knit_print.

Print the flextable object in the rmarkdown’s chunk as demonstrated in this document (…generated from an R Markdown document).

  
    ---
    title: 'flextable formatting'
    output: rmarkdown::html_document
    ---
    
    
    > this is how to print a flextable in a R Markdown document
    
    
    ```{r}
    library(flextable)
    ft <- flextable(head(mtcars))
    ft <- autofit(ft)
    ft
    ```

pandoc versions

Supported formats require some minimum pandoc versions:

Output format	pandoc version
HTML	>= 1.12
Word (docx)	>= 2.0
PowerPoint (pptx)	>= 2.4
PDF	>= 1.12

Notes about rmarkdown::word_document

This note is only relevant when using flextable in an R Markdown document with Word output.

In some context, officedown::rdocx_document() will have to be used instead of rmarkdown::word_document(). This is because Word doesn’t store hyperlinks or images in the main document but stores references. This is not managed by rmarkdown unless officedown::rdocx_document() is used.

If you don’t add images or hyperlinks in a flextable rendered by officedown::rdocx_document() then you can forget about that.

Notes about rmarkdown::pdf_document

The PDF version of the flextable ignore some features of flextable, here is the list of unsupported/ignored options:

padding is not taken into account (it is instead recommended to use the arguments ft.tabcolsep and ft.arraystretch),
the borders can only be full (no dash for example),
the height of the lines cannot be defined.

In order to be able to change latex font in a flextable, PDF engine should be specified by adding latex_engine: xelatex in the YAML header of the R Markdown document. The default one pdflatex does not enable the use of system fonts.

PowerPoint or Word documents with officer

Simple export

Use function save_as_docx or save_as_pptx that lets users export flextable objects to PowerPoint or Word documents. Note save_as_html is also available.

docx_file <- tempfile(fileext = ".docx")
pptx_file <- tempfile(fileext = ".pptx")
html_file <- tempfile(fileext = ".html")
# docx_file <- "example.docx"
# pptx_file <- "example.pptx"
save_as_docx("my table" = ft, path = docx_file)
save_as_docx("my table" = ft, path = pptx_file)
save_as_html("my table" = ft, path = html_file, title = "example")

In an interactive session

If you have a Word or PowerPoint client on your machine, you can use the print method with argument preview set to “pptx” or “docx”. It will produce and open a document where the table will be printed and ready to go to your clipboard.

print(ft, preview = "docx")
print(ft, preview = "pptx")

With package officer

To add these objects in PowerPoint or Word documents, use functions:

ph_with() (PowerPoint)
body_add_flextable() (Word)

library(officer)

The following is producing a PowerPoint document:

ppt <- read_pptx()
ppt <- add_slide(ppt, layout = "Title and Content", master = "Office Theme")
ppt <- ph_with(ppt, value = ft, location = officer::ph_location_left()) 

print(ppt, target = "example.pptx")

The following is producing a Word document:

doc <- read_docx()
doc <- body_add_flextable(doc, value = ft)
print(doc, target = "example.docx")