2.5 Tables

For now, the most convenient way to generate a table is the function knitr::kable(), because there are some internal tricks in knitr to make it work with bookdown and users do not have to know anything about these implementation details. We will explain how to use other packages and functions later in this section.

Like figures, tables with captions will also be numbered and can be referenced. The kable() function will automatically generate a label for a table environment, which is the prefix tab: plus the chunk label. For example, the table label for a code chunk with the label foo will be tab:foo, and we can still use the syntax \@ref(label) to reference the table. Table 2.2 is a simple example.

knitr::kable(
  head(mtcars[, 1:8], 10), booktabs = TRUE,
  caption = 'A table of the first 10 rows of the mtcars data.'
)
TABLE 2.2: A table of the first 10 rows of the mtcars data.
mpg cyl disp hp drat wt qsec vs
Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0
Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0
Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1
Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1
Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0
Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1
Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0
Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1
Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1
Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1

If you want to put multiple tables in a single table environment, wrap the data objects (usually data frames in R) into a list. See Table 2.3 for an example.

knitr::kable(
  list(
    head(iris[, 1:2], 3),
    head(mtcars[, 1:3], 5)
  ),
  caption = 'A Tale of Two Tables.', booktabs = TRUE
)
TABLE 2.3: A Tale of Two Tables.
Sepal.Length Sepal.Width
5.1 3.5
4.9 3.0
4.7 3.2
mpg cyl disp
Mazda RX4 21.0 6 160
Mazda RX4 Wag 21.0 6 160
Datsun 710 22.8 4 108
Hornet 4 Drive 21.4 6 258
Hornet Sportabout 18.7 8 360

When you do not want a table to float in PDF, you may use the LaTeX package longtable, which can break a table across multiple pages. To use longtable, pass longtable = TRUE to kable(), and make sure to include \usepackage{longtable} in the LaTeX preamble (see Section 4.1 for how to customize the LaTeX preamble). Of course, this is irrelevant to HTML output, since tables in HTML do not need to float.

knitr::kable(
  iris[1:55, ], longtable = TRUE, booktabs = TRUE,
  caption = 'A table generated by the longtable package.'
)
TABLE 2.4: A table generated by the longtable package.
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
5.4 3.7 1.5 0.2 setosa
4.8 3.4 1.6 0.2 setosa
4.8 3.0 1.4 0.1 setosa
4.3 3.0 1.1 0.1 setosa
5.8 4.0 1.2 0.2 setosa
5.7 4.4 1.5 0.4 setosa
5.4 3.9 1.3 0.4 setosa
5.1 3.5 1.4 0.3 setosa
5.7 3.8 1.7 0.3 setosa
5.1 3.8 1.5 0.3 setosa
5.4 3.4 1.7 0.2 setosa
5.1 3.7 1.5 0.4 setosa
4.6 3.6 1.0 0.2 setosa
5.1 3.3 1.7 0.5 setosa
4.8 3.4 1.9 0.2 setosa
5.0 3.0 1.6 0.2 setosa
5.0 3.4 1.6 0.4 setosa
5.2 3.5 1.5 0.2 setosa
5.2 3.4 1.4 0.2 setosa
4.7 3.2 1.6 0.2 setosa
4.8 3.1 1.6 0.2 setosa
5.4 3.4 1.5 0.4 setosa
5.2 4.1 1.5 0.1 setosa
5.5 4.2 1.4 0.2 setosa
4.9 3.1 1.5 0.2 setosa
5.0 3.2 1.2 0.2 setosa
5.5 3.5 1.3 0.2 setosa
4.9 3.6 1.4 0.1 setosa
4.4 3.0 1.3 0.2 setosa
5.1 3.4 1.5 0.2 setosa
5.0 3.5 1.3 0.3 setosa
4.5 2.3 1.3 0.3 setosa
4.4 3.2 1.3 0.2 setosa
5.0 3.5 1.6 0.6 setosa
5.1 3.8 1.9 0.4 setosa
4.8 3.0 1.4 0.3 setosa
5.1 3.8 1.6 0.2 setosa
4.6 3.2 1.4 0.2 setosa
5.3 3.7 1.5 0.2 setosa
5.0 3.3 1.4 0.2 setosa
7.0 3.2 4.7 1.4 versicolor
6.4 3.2 4.5 1.5 versicolor
6.9 3.1 4.9 1.5 versicolor
5.5 2.3 4.0 1.3 versicolor
6.5 2.8 4.6 1.5 versicolor

Pandoc supports several types of Markdown tables, such as simple tables, multiline tables, grid tables, and pipe tables. What knitr::kable() generates is a simple table like this:

Table: A simple table in Markdown.

 Sepal.Length   Sepal.Width   Petal.Length   Petal.Width
-------------  ------------  -------------  ------------
          5.1           3.5            1.4           0.2
          4.9           3.0            1.4           0.2
          4.7           3.2            1.3           0.2
          4.6           3.1            1.5           0.2
          5.0           3.6            1.4           0.2
          5.4           3.9            1.7           0.4

You can use any types of Markdown tables in your document. To be able to cross-reference a Markdown table, it must have a labeled caption of the form Table: (\#label) Caption here, where label must have the prefix tab:, e.g., tab:simple-table.

If you decide to use other R packages to generate tables, you have to make sure the label for the table environment appears in the beginning of the table caption in the form (\#label) (again, label must have the prefix tab:). You have to be very careful about the portability of the table generating function: it should work for both HTML and LaTeX output automatically, so it must consider the output format internally (check knitr::opts_knit$get('pandoc.to')). When writing out an HTML table, the caption must be written in the <caption></caption> tag. For simple tables, kable() should suffice. If you have to create complicated tables (e.g., with certain cells spanning across multiple columns/rows), you will have to take the aforementioned issues into consideration.