Lemon print -- pretty printing data frames and tables"

In lemon: Freshing Up your 'ggplot2' Plots

This vignette demonstrates how load the lemon package automatically enables pretty printing of data frames with knitr's kable.

The beauty of defining the function knit_print.data.frame is that when working with R Notebooks in R, the editor can output the data frame dynamically, while ensuring that the knitted document also has the

library(knitr)
library(stringr)

knitr::opts_chunk$set(fig.height=4, fig.width=6, verbatim=FALSE,
                      cache=FALSE, autodep = TRUE, cache.path='lemon_print-cache/')

# Show chunk verbatim
# Source: https://stackoverflow.com/questions/19908158/show-an-r-markdown-chunk-in-the-final-output
# Set verbatim option as last and it will not be printed. ;)
hook_source_def = knit_hooks$get('source')
knit_hooks$set(source = function(x, options){
  if (!is.null(options$verbatim) && options$verbatim){
    opts = gsub(",\\s*verbatim\\s*=\\s*TRUE\\s*", "", options$params.src)
    bef = sprintf('\n\n    ```r\n', opts, "\n")
    stringr::str_c(bef, paste(knitr:::indent_block(x, "    "), collapse = '\n'), "\n    ```\n\n")
  } else {
     hook_source_def(x, options)
  }
})

First we load some data and show the top.

data(USArrests)
head(USArrests)

Now load lemon and set the lemon_print functions.

library(lemon)
knit_print.data.frame <- lemon_print

The same view is now nicely printed!

head(USArrests)

Notice how we specified kable arguments directly as chunk-options.

How it works

knitr uses a S3 generic function, knit_print, to print objects. Method dispatching in R means that by defining a function, say knit_print.data.frame, calling knit_print(df) will call our function if df was a data frame.

To have knitr use our function when outputting a data frame, we define the function knit_print.data.frame (and similar for data frames passed through dplyr functions, i.e tbl_df and grouped_df).

Disabling the function is by usual chunk options, render = normal_print. check ?knit_print.

Disabling the functions.

head(USArrests)

You can still ask for kable.

kable(head(USArrests),caption='Normal `kable` usage.')

It uses kable

We have mentioned kable a couple of times. That is because the lemon_print for data frames uses kable of the knitr package.

Some common arguments:

• caption: Table caption. See examples in demonstration.
• align: Vector of column alignments with 'l', 'c', and 'r'. Or, a single element, i.e. c('c','l','r') = 'clr').
• row.names: A logical value indicating whether to include row names.
• col.names: A character vector of column names to be used in the table.

Why does it matter

The second code block, when edited in RStudio, would look like this: And, as demonstrated, the rendered document has the data frame printed nicely.

If we do not wish this behaviour, but still use kable,

kable(head(USArrests))

RStudio would look like this:

Other objects covered

Summaries are nicely formatted, but these require setting the S3 method for table.

knit_print.table <- lemon_print
summary(USArrests)

Cross-tabulations are however not nicely formatted.

head(mtcars)
with(mtcars, table(cyl, gear))

dplyr

library(dplyr)
knit_print.tbl <- lemon_print

mtcars %>% group_by(cyl) %>% summarise(mean(disp))

lemon documentation built on Nov. 7, 2023, 5:06 p.m.