Word Wrap Text to Format Paragraphs

This function breaks text paragraphs into lines, of total width (if it is possible) at most given width.

Usage

stri_wrap(
  str,
  width = floor(0.9 * getOption("width")),
  cost_exponent = 2,
  simplify = TRUE,
  normalize = TRUE,
  normalise = normalize,
  indent = 0,
  exdent = 0,
  prefix = "",
  initial = prefix,
  whitespace_only = FALSE,
  use_length = FALSE,
  locale = NULL
)

Arguments

str: character vector of strings to reformat
width: single integer giving the suggested maximal total width/number of code points per line
cost_exponent: single numeric value, values not greater than zero will select a greedy word-wrapping algorithm; otherwise this value denotes the exponent in the cost function of a (more aesthetic) dynamic programming-based algorithm (values in [2, 3] are recommended)
simplify: single logical value, see Value
normalize: single logical value, see Details
normalise: alias of normalize
indent: single non-negative integer; gives the indentation of the first line in each paragraph
exdent: single non-negative integer; specifies the indentation of subsequent lines in paragraphs
prefix, initial: single strings; prefix is used as prefix for each line except the first, for which initial is utilized
whitespace_only: single logical value; allow breaks only at white-spaces? if FALSE, ICU's line break iterator is used to split text into words, which is suitable for natural language processing
use_length: single logical value; should the number of code points be used instead of the total code point width (see stri_width)?
locale: NULL or '' for text boundary analysis following the conventions of the default locale, or a single string with locale identifier, see stringi-locale

Value

If simplify is TRUE, then a character vector is returned. Otherwise, you will get a list of length(str) character vectors.

Details

Vectorized over str.

If whitespace_only is FALSE, then ICU's line-BreakIterator is used to determine text boundaries where a line break is possible. This is a locale-dependent operation. Otherwise, the breaks are only at white-spaces.

Note that Unicode code points may have various widths when printed on the console and that this function, by default, takes that into account. By changing the state of the use_length argument, this function starts to act as if each code point was of width 1.

If normalize is FALSE, then multiple white spaces between the word boundaries are preserved within each wrapped line. In such a case, none of the strings can contain \r, \n, or other new line characters, otherwise you will get an error. You should split the input text into lines or, for example, substitute line breaks with spaces before applying this function.

If normalize is TRUE, then all consecutive white space (ASCII space, horizontal TAB, CR, LF) sequences are replaced with single ASCII spaces before actual string wrapping. Moreover, stri_split_lines and stri_trans_nfc is called on the input character vector. This is for compatibility with strwrap.

The greedy algorithm (for cost_exponent being non-positive) provides a very simple way for word wrapping. It always puts as many words in each line as possible. This method – contrary to the dynamic algorithm – does not minimize the number of space left at the end of every line. The dynamic algorithm (a.k.a. Knuth's word wrapping algorithm) is more complex, but it returns text wrapped in a more aesthetic way. This method minimizes the squared (by default, see cost_exponent) number of spaces (raggedness) at the end of each line, so the text is mode arranged evenly. Note that the cost of printing the last line is always zero.

References

D.E. Knuth, M.F. Plass, Breaking paragraphs into lines, Software: Practice and Experience 11(11), 1981, pp. 1119–1184.

Author

Marek Gagolewski and other contributors

Examples

s <- stri_paste(
   'Lorem ipsum dolor sit amet, consectetur adipisicing elit. Proin ',
   'nibh augue, suscipit a, scelerisque sed, lacinia in, mi. Cras vel ',
   'lorem. Etiam pellentesque aliquet tellus.')
cat(stri_wrap(s, 20, 0.0), sep='\n') # greedy
#> Lorem ipsum dolor
#> sit amet,
#> consectetur
#> adipisicing elit.
#> Proin nibh augue,
#> suscipit a,
#> scelerisque sed,
#> lacinia in, mi. Cras
#> vel lorem. Etiam
#> pellentesque aliquet
#> tellus.
cat(stri_wrap(s, 20, 2.0), sep='\n') # dynamic
#> Lorem ipsum
#> dolor sit amet,
#> consectetur
#> adipisicing elit.
#> Proin nibh augue,
#> suscipit a,
#> scelerisque sed,
#> lacinia in, mi. Cras
#> vel lorem. Etiam
#> pellentesque aliquet
#> tellus.
cat(stri_pad(stri_wrap(s), side='both'), sep='\n')
#>   Lorem ipsum dolor sit amet, consectetur adipisicing elit. Proin nibh  
#>   augue, suscipit a, scelerisque sed, lacinia in, mi. Cras vel lorem.   
#>                    Etiam pellentesque aliquet tellus.