Programmatically creating Markdown tables in R with KnitR

There are functions in the pander package:

> library(pander)
> pandoc.table(head(iris)[, 1:3])

-------------------------------------------
 Sepal.Length   Sepal.Width   Petal.Length 
-------------- ------------- --------------
     5.1            3.5           1.4      

     4.9             3            1.4      

     4.7            3.2           1.3      

     4.6            3.1           1.5      

      5             3.6           1.4      

     5.4            3.9           1.7      
-------------------------------------------

Two packages that will do this are pander

library(devtools)
install_github('pander', 'Rapporter')

Or ascii

pander is a slightly different approach to report construction, (but can be useful for this feature).

ascii will allow you to print with type = 'pandoc (or various other markdown flavours)

library(ascii)
print(ascii(head(iris[,1:3])), type = 'pandoc')



    **Sepal.Length**   **Sepal.Width**   **Petal.Length**  
--- ------------------ ----------------- ------------------
1   5.10               3.50              1.40              
2   4.90               3.00              1.40              
3   4.70               3.20              1.30              
4   4.60               3.10              1.50              
5   5.00               3.60              1.40              
6   5.40               3.90              1.70              
--- ------------------ ----------------- ------------------

Note that in both these cases, it is directed towards using pandoc to convert from markdown to your desired document type, however using style='rmarkdown' will create tables that are compatible with this markdown package and inbuilt conversion in rstudio.

Now knitr (since version 1.3) package include the kable function for a creation tables:

> library(knitr)
> kable(head(iris[,1:3]), format = "markdown")
|  Sepal.Length|  Sepal.Width|  Petal.Length|
|-------------:|------------:|-------------:|
|           5,1|          3,5|           1,4|
|           4,9|          3,0|           1,4|
|           4,7|          3,2|           1,3|
|           4,6|          3,1|           1,5|
|           5,0|          3,6|           1,4|
|           5,4|          3,9|           1,7|

UPDATED: if you get raw markdown in a document try setup results = "asis" chunk option.

Just wanted to update this with what I settled on doing. I am using the hwriter package right now to print out tables, and using the row.* and col.* features to put CSS classes on to different elements. Then, I wrote custom CSS to make my display as I wanted it. So, here's an example in case anyone else is dealing with something similar.

First, create a file that will do the knitting and change the Markdown into HTML:

FILE: file_knit.r
#!/usr/bin/env Rscript

library(knitr)
library(markdown)

knit("file.Rmd")
markdownToHTML("file.md","file.html",stylesheet="~/custom.css")

Next, create the actual Markdown file:

FILE: file.Rmd
Report of Fruit vs. Animal Choices
==================================

This is a report of fruit vs. animal choices.

```{r echo=FALSE,results='asis'}
library(hwriter)
set.seed(9850104)
my.df <- data.frame(Var1=sample(x=c("Apple","Orange","Banana"),size=40,replace=TRUE),
                    Var2=sample(x=c("Dog","Cat","Bunny"),size=40,replace=TRUE))

tbl1 <- table(my.df$Var1,my.df$Var2)

tbl1 <- cbind(tbl1,rowSums(tbl1))
tbl1 <- rbind(tbl1,colSums(tbl1))

colnames(tbl1)[4] <- "TOTAL"
rownames(tbl1)[4] <- "TOTAL"

# Because I used results='asis' for this chunk, I can just use cat() and hwrite() to 
# write out the table in HTML. Using hwrite()'s row.* function, I can assign classes
# to the various table elements.
cat(hwrite(tbl1,
           border=NA,
           table.class="t1",
           row.class=list(c("header col_first","header col","header col","header col", "header col_last"),
                          c("col_first","col","col","col","col_last"),
                          c("col_first","col","col","col","col_last"),
                          c("col_first","col","col","col","col_last"),
                          c("footer col_first","footer col","footer col","footer col","footer col_last"))))
```

Finally, just create a custom CSS file.

FILE: custom.css
body {
  font-family: sans-serif;
  background-color: white;
  font-size: 12px;
  margin: 20px;
}

h1 {font-size:1.5em;}

table {
  border: solid;
  border-color: black;
  border-width: 2px;
  border-collapse: collapse;
  margin-bottom: 20px;
  text-align: center;
  padding: 0px;
}

.t1 .header {
  color: white;
  background-color: black;
  border-bottom: solid;
  border-color: black;
  border-width: 2px;
  font-weight: bold;
}

.t1 .footer {
  border-top: solid;
  border-color: black;
  border-width: 2px;
}

.t1 .col_first {
  border-right: solid;
  border-color: black;
  border-width: 2px;
  text-align: left;
  font-weight: bold;
  width: 75px;
}

.t1 .col {
  width: 50px;
}

.t1 .col_last {
  width: 50px;
  border-left: solid;
  border-color: black;
  border-width: 2px;
}

Executing ./file_knit.r gives me file.html, which looks like this:

So, hopefully this might be helpful to others who want a bit more formatting in Markdown output!