epub_reorder {epubr}

Reorder sections

Description

Reorder text sections in an e-book based on a user-provided function.

Usage

epub_reorder(data, .f, pattern)

Arguments

data

a data frame created by epub.

.f

a scalar function to determine a single row index based on a matched regular expression. It must take two strings, the text and the pattern, and return a single number. See examples.

pattern

regular expression passed to .f.

Details

Many e-books have chronologically ordered sections based on quality metadata. This results in properly book sections in the nested data frame. However, some poorly formatted e-books have their internal sections occur in an arbitrary order. This can be frustrating to work with when doing text analysis on each section and where order matters.

This function addresses this case by reordering the text sections in the nested data frame based on a user-provided function that re-indexes the data frame rows based on their content. In general, the approach is to find something in the content of each section that describes the section order. For example, epub_recombine can use a regular expression to identify chapters. Taking this a step further, epub_reorder can use a function that works with the same information to reorder the rows.

It is enough in the former case to identify where in the text the pattern occurs. There is no need to extract numeric ordering from it. The latter takes more effort. In the example EPUB file included in epubr, chapters can be identified using a pattern of the word CHAPTER in capital letters followed by a space and then some Roman numerals. The user must provide a function that would parse the Roman numerals in this pattern so that the rows of the data frame can be reordered properly.

Value

a data frame

Examples

file <- system.file("dracula.epub", package = "epubr")
x <- epub(file) # parse entire e-book
x <- epub_recombine(x, "CHAPTER [IVX]+", sift = list(n = 1000)) # clean up

library(dplyr)
set.seed(1)
x$data[[1]] <- sample_frac(x$data[[1]]) # randomize rows for example
x$data[[1]]

f <- function(x, pattern) as.numeric(as.roman(gsub(pattern, "\\1", x)))
x <- epub_reorder(x, f, "^CHAPTER ([IVX]+).*")
x$data[[1]]