HTML Tables

Duncan Murdoch

January 17, 2016

This short R Markdown document illustrates how to use tables in HTML.

Initializing

First, you need to load tables. Packages that it uses print banner messages, so you’ll usually want to set a chunk option of message=FALSE.

library(tables)

The table is now constructed in the usual way.

X <- rnorm(125, sd=100)
Group <- factor(sample(letters[1:5], 125, rep=TRUE))
tab <- tabular( Group ~ (N=1)+Format(digits=2)*X*((Mean=mean) + Heading("Std Dev")*sd) )

In an R Markdown document, you don’t want each table to output the HTML document header, so turn off those options:

table_options(htmloptions(head=FALSE))

Inserting a Table

There are two ways to insert a table into a knitr/rmarkdown document. Since tables version 0.8.4, you can just print the object, and it will be automatically formatted according to the current table_options():

tab
    X
Group N Mean Std Dev
a 21 -6.9 99.5
b 29 -5.3 121.3
c 28 -24.8 110.1
d 25 -9.9 83.4
e 22 -5.3 113.4

The previous behaviour required an explicit call to the html() function, and knitr option results = 'asis' for the chunk. To require the older method, use table_options(knit_print = FALSE):

table_options(knit_print = FALSE)
tab        # This chunk uses the default results = 'markup'
##                        
##           X            
##  Group N  Mean  Std Dev
##  a     21  -6.9  99.5  
##  b     29  -5.3 121.3  
##  c     28 -24.8 110.1  
##  d     25  -9.9  83.4  
##  e     22  -5.3 113.4
html(tab)  # This chunk uses results = 'asis'
    X
Group N Mean Std Dev
a 21 -6.9 99.5
b 29 -5.3 121.3
c 28 -24.8 110.1
d 25 -9.9 83.4
e 22 -5.3 113.4

In either case, some styling information needs to be included in the document. Ideally this should be in the header, but it can be inserted anywhere by calling writeCSS with results = 'asis':

writeCSS()

Improving the Look

The default justification makes the columns of numbers look messy. You can set the justification to the right, but the headers look wrong:

table_options(htmloptions(head = FALSE, justification = "r", knit_print = TRUE))
tab
    X
Group N Mean Std Dev
a 21 -6.9 99.5
b 29 -5.3 121.3
c 28 -24.8 110.1
d 25 -9.9 83.4
e 22 -5.3 113.4

The best look comes with the pad = TRUE option. This adds nonbreaking spaces around the numbers so that centering looks good. It also changes the hyphens to proper minus signs:

table_options(htmloptions(head = FALSE, justification = "c", pad = TRUE))
tab
    X
Group N Mean Std Dev
a 21   −6.9   99.5
b 29   −5.3  121.3
c 28  −24.8  110.1
d 25   −9.9   83.4
e 22   −5.3  113.4

Unfortunately, if you cut this table and paste it into a spreadsheet, the spaces and minus signs probably won’t be understood. I don’t know how to get everything we want :-(.

Fine tuning

This document uses the default CSS from table_options()$CSS. If you are producing an html_document, it should be okay. It does not look quite right in a slidy_presentation, and is no good at all in an ioslides_presentation. Furthermore, you might not agree with my design choices.

In any of these cases, you should substitute your own CSS. You will need to modify the default one, and can use it as the CSS argument to writeCSS(), or set it as a new default in table_options().

Here is the default setting:

<style>
#ID .Rtable thead, .Rtable .even {
  background-color: inherit;
}
#ID .left   { text-align:left; }
#ID .center { text-align:center; }
#ID .right  { text-align:right; }
#ID .Rtable, #ID .Rtable thead { 
  border-collapse: collapse;
  border-style: solid;
  border-width: medium 0;
  border-color: inherit;
}
#ID .Rtable th, #ID .Rtable td {
  padding-left: 0.5em;
  padding-right: 0.5em;
  border-width: 0;
}
</style>

Note that the #ID values will be replaced with the id string given in writeCSS(), and html() has a corresponding argument to allow you to make changes for one specific table. If you are using the newer form of display with table_options(knit_print = TRUE), you can get customized display for one table by also using table_options(doCSS = TRUE). For example,

table_options(CSS =
"<style>
#ID .center { 
  text-align:center;
  background-color: aliceblue;
}
</style>", doCSS = TRUE)
tab
    X
Group N Mean Std Dev
a 21   −6.9   99.5
b 29   −5.3  121.3
c 28  −24.8  110.1
d 25   −9.9   83.4
e 22   −5.3  113.4
table_options(doCSS = FALSE)
tab
    X
Group N Mean Std Dev
a 21   −6.9   99.5
b 29   −5.3  121.3
c 28  −24.8  110.1
d 25   −9.9   83.4
e 22   −5.3  113.4

kableExtra support

The kableExtra package contains a large number of functions to customize the look of tables generated by the knitr::kable() function. These can also be made to work with tables from this package, using the toKable() function. For example,

library(magrittr)
library(kableExtra)
## Registered S3 method overwritten by 'rvest':
##   method            from
##   read_xml.response xml2
toKable(tab) %>% 
  kable_styling("striped", position = "float_right", full_width = FALSE) %>%
  add_header_above(c("Row Label" = 1, "Statistics" = 3)) %>%
  column_spec(4, color = "red") %>%
  row_spec(1, color = "blue") %>%
  group_rows("Subgroup", 3, 5)
Row Label
Statistics
    X
Group N Mean Std Dev
a 21   −6.9   99.5
b 29   −5.3  121.3
Subgroup
c 28  −24.8  110.1
d 25   −9.9   83.4
e 22   −5.3  113.4

There are conflicts between the styling options from kableExtra and the ones specified in table_options()$CSS; some modifications might be needed to make everything work. For instance, the code above requests striping, but that did not show up. Experimentation may be needed!