flextable layout

flextable layout can be easily managed. A set of functions will let you merge cells, add title rows, add footer notes, change the withs or heights.


flextable col_keys

Parameter col_keys of function flextable define the variables to display and their order.

data <- iris[c(1:3, 51:53, 101:104),]
myft <- flextable(data, col_keys = c("Species", "Sepal.Length", "Petal.Length") )

If parameter col_keys has variables that are not existing in the dataset, they will be considered as blank columns and can be used as separators (in fact they can be use as you want, there is only no mapping of data associated).

myft <- flextable(
  data = data, 
  col_keys = c("Species", "col_1", "Sepal.Length", "Petal.Length") )
myft <- theme_vanilla(myft)
myft <- autofit(myft)
myft <- empty_blanks(myft)

col_keys default values are the names of the data.frame used to fill the flextable.

Change labels

Use set_header_labels() to replace labels of the bottom row of header. When the flextable is created, their values are the column names of the data.frame.

ft <- flextable( head( iris ) ) 
ft <- set_header_labels(ft, Sepal.Length = "Sepal length", 
    Sepal.Width = "Sepal width", Petal.Length = "Petal length",
    Petal.Width = "Petal width" )

New header rows can be added at the top or bottom of the header. This part in documented in part Manage headers and footers.

Under the hood, the names are in a single row data.frame associated with the header part of the flextable. You can add new rows later, they will be binded to that data.frame.

Cell merging

To illustrate functions, we will use a basic flextable example:

dat <- data.frame(
  letters1 = c("a", "b", "b", "c"), 
  letters2 = c("d", "e", "b", "b"), 
  number = 1:4, stringsAsFactors = FALSE )

myft <- flextable(dat)
myft <- theme_box(myft)

vertical merging of similar values

merge_v() will merge adjacent duplicated cells for each column of the selection.

merge_v(myft, j = ~ letters1 + letters2 )

horizontal merging of similar values

merge_h() will merge adjacent duplicated cells for each row of the selection.


horizontal merging of columns

Function merge_h_range is close to the previous one but merge all colums between a range of columns.

  i =  ~ number < 3, 
  j1 = "letters1", j2 = "letters2")

general merging function

merge_at() will merge cells for a given continuous selection of rows and cells. The result is a single cell.

myft %>% 
    i = 1:2, j = 1:2)

Note that the content that is rendered is not the result of the concatenation of each paragraphs contained into the merge cells. Only one paragraph will be kept, the top left one of all merge cells.

delete merging informations

If you want to get rid of all merging (i.e. for development purposes), use merge_none():


Borders and merging

When cells are merged, the rendered borders will be those of the first cell. If a column is made of three merged cells, the bottom border that will be seen will be the bottom border of the first cell in the column. From a user point of view, this is wrong, the bottom should be the one defined for cell 3. Function fix_border_issues is trying to fix that issue.

ft <- data.frame(a = 1:5, b = 6:10) %>%
  flextable() %>% theme_box() %>%
  merge_at(i = 4:5, j = 1, part = "body") %>%
  hline(i = 5, part = "body",
        border = fp_border(color = "orange", width = 3) )

Manage headers and footers

Use one of the following functions to add an header row or a footer row:

We will mainly demonstrate headers but same can be apply with footers.

The operation below is changing labels that will be displayed instead of the original values (the names of dataset).

ft <- flextable( head( iris ) ) 
ft <- set_header_labels(ft, Sepal.Length = "Sepal", 
    Sepal.Width = "Sepal", Petal.Length = "Petal",
    Petal.Width = "Petal" )
# merge them 
ft <- merge_at(ft, i = 1, j = 1:2, part = "header")
ft <- merge_at(ft, i = 1, j = 3:4, part = "header")

Now let’s add new row of labels.

Add a row of labels

ft <- add_header_row(ft, 
  values = c("", "length", "width", "length", "width"), top = FALSE )
ft <- theme_box(ft)

Add lines of text

ft <- add_header_lines(ft, 
  values = c("this is a first line", 
     "this is a second line") ) 
ft <- theme_box(ft)

Define headers with a reference table

Use set_header_df() with a data.frame as parameter. Columns of the dataset will be transposed and joined using a key column.

  1. The reference table

Variable col_keys define key values to match with flextable column keys (defined by argument col_keys of flextable() function).

This key column will not be displayed. Other variables will added as rows. Note that variables names are not displayed.

typology <- data.frame(
  col_keys = c( "Sepal.Length", 
    "Sepal.Width", "Petal.Length",
    "Petal.Width", "Species" ),
  type = c("double", "double", "double", 
    "double", "factor"),
  what = c("Sepal", "Sepal", "Petal", 
    "Petal", "Species"),
  measure = c("Length", "Width", "Length", 
    "Width", "Species"),
  stringsAsFactors = FALSE )
  1. Use it as header rows

Then use set_header_df() with parameter key. key is the name of the column used to permform the join operation.

Order of columns matters, first column will be first row, second one will be the second row, etc.

ft <- flextable( head( iris ) )
ft <- set_header_df( ft, mapping = typology, key = "col_keys" )

ft <- merge_h(ft, part = "header")
ft <- merge_v(ft, part = "header")

ft <- theme_booktabs(ft)
ft <- autofit(ft)
ft <- fix_border_issues(ft)

Table width

By default, table width is fixed. This setting allows to have the same rendering with Word, HTML and PowerPoint formats.

You can use another setting with function set_table_properties() when argument layout is set to ‘autofit’, an algorithm implemented by HTML and Word.

When layout is set to autofit, you can also size the table along an available width with argument width (default to 1 that means 100% of the available width).

ft <- qflextable(head(airquality))
set_table_properties(ft, width = .5, layout = "autofit")
set_table_properties(ft, width = 1, layout = "autofit")

Cell widths and heights

This only applies when layout is “fixed” - see Table width

The default sizes of flextable columns and rows are set by default values. This will drive to inadequate rows heights and columns widths in some cases. You can use function dim to get flextable dimensions.

ft_base <- flextable(head(mtcars))
ft_base <- theme_vader(ft_base)
dim(ft_base) #> $widths #> mpg cyl disp hp drat wt qsec vs am gear carb #> 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 #> #> $heights #> [1] 0.25 0.25 0.25 0.25 0.25 0.25 0.25

Pretty dimensions

Function dim_pretty() is computing optimized widths and heights.

#> $widths
#>  [1] 0.4629178 0.3428006 0.4537218 0.3891873 0.4259711 0.3428006 0.4909939
#>  [8] 0.2964952 0.3519965 0.4631619 0.4631619
#> $heights
#> [1] 0.2669542 0.2313097 0.2313097 0.2313097 0.2313911 0.2313097 0.2313911

Adjusts automatically cell widths and heights

Function autofit() optimises widths and heights of the flextable. This function makes compact tables.

autofit was not my biggest naming idea as users are thinking it is the ‘Microsoft Word feature’ (see set_table_properties)

ft <- autofit(ft_base, add_w = 0, add_h = 0)

#> $widths
#>       mpg       cyl      disp        hp      drat        wt      qsec        vs 
#> 0.4629178 0.3428006 0.4537218 0.3891873 0.4259711 0.3428006 0.4909939 0.2964952 
#>        am      gear      carb 
#> 0.3519965 0.4631619 0.4631619 
#> $heights
#> [1] 0.2669542 0.2313097 0.2313097 0.2313097 0.2313911 0.2313097 0.2313911

Soft returns (a line break in a paragraph) support : function autofit and dim_pretty do not support soft returns and may return wrong results (will be considered as "").

Adjusts manually cell widths and heights

Function width() and height() let you control dimensions of a flextable. height_all() is an helper function to set the same height to each part of the table.

ft <- hrule(ft, rule = "exact")
ft <- valign(ft, valign = "top")
ft <- width(ft, width = .5)
ft <- width(ft, j = ~ mpg + disp, width = 1.5)
ft <- height_all( ft, height = .6 )
ft <- height( ft, i = 3, height = 1 )

Function height() has no effect when the rule for line height is set to “auto”, which is the default case, except with PowerPoint which does not support this automatic line height adjustment feature. You can define that rule with function hrule.

Function hrule support three options :