template.replace: Replace Values in a Template Text

Description

template.replace replaces keys within special markups with values in a so-called template file. Pieces of R code can be put into the markups of the template file, and are evaluated during the replacement.

Usage

template.replace(text, replacement, eval = FALSE,
                 key.pattern = NULL, code.pattern = NULL)

Arguments

text: vector of character strings, the template text.
replacement: the list values to replace in text.
eval: boolean, TRUE if the code within code.pattern has to be evaluated, FALSE otherwise.
key.pattern: custom pattern for key replacement (see below)
code.pattern: custom pattern for code replacement (see below)

Author

Gilles Pujol

Details

In most cases, a computational code reads its inputs from a text file. A template file is like an input file, but where some missing values, identified with generic keys, will be replaced by specific values.

By default, the keys are enclosed into markups of the form $(KEY).

Code to be interpreted with R can be put in the template text. Pieces of code must be enclosed into markups of the form @{CODE}. This is useful for example for formating the key values (see example). For interpreting the code, set eval = TRUE.

Users can define custom patterns. These patterns must be perl-compatible regular expressions (see regexpr. The default ones are:

key.pattern = "\\$\\(KEY\\)"
code.pattern = "@\\{CODE\\}"

Note that special characters have to be escaped both (one for perl, one for R).

Examples

Run this code

txt <- c("Hello $(name)!", "$(a) + $(b) = @{$(a)+$(b)}",
         "pi = @{format(pi,digits=5)}")
replacement <- list(name = "world", a = 1, b = 2)
# 1. without code evaluation:
txt.rpl1 <- template.replace(txt, replacement)
print(txt.rpl1)
# 2. with code evalutation:
txt.rpl2 <- template.replace(txt, replacement, eval = TRUE)
print(txt.rpl2)