Introduction to bracer

Table of Contents

• Overview
• Examples
• Installation
• Limitations of pure R parser and alternative javascript parser

Overview

bracer provides support for performing brace expansions on strings in R.

Examples

library("bracer")
options(bracer.engine = "r")
expand_braces("Foo{A..F}")

## [1] "FooA" "FooB" "FooC" "FooD" "FooE" "FooF"

expand_braces("Foo{01..10}")

##  [1] "Foo01" "Foo02" "Foo03" "Foo04" "Foo05" "Foo06" "Foo07" "Foo08" "Foo09"
## [10] "Foo10"

expand_braces("Foo{A..E..2}{1..5..2}")

## [1] "FooA1" "FooA3" "FooA5" "FooC1" "FooC3" "FooC5" "FooE1" "FooE3" "FooE5"

expand_braces("Foo{-01..1}")

## [1] "Foo-01" "Foo000" "Foo001"

expand_braces("Foo{{d..d},{bar,biz}}.{py,bash}")

## [1] "Food.py"     "Food.bash"   "Foobar.py"   "Foobar.bash" "Foobiz.py"  
## [6] "Foobiz.bash"

expand_braces is vectorized and returns one big character vector of all the brace expansions. str_expand_braces is an alternative that returns a list of character vectors.

expand_braces(c("Foo{A..F}", "Bar.{py,bash}", "{{Biz}}"))

## [1] "FooA"     "FooB"     "FooC"     "FooD"     "FooE"     "FooF"     "Bar.py"  
## [8] "Bar.bash" "{{Biz}}"

str_expand_braces(c("Foo{A..F}", "Bar.{py,bash}", "{{Biz}}"))

## [[1]]
## [1] "FooA" "FooB" "FooC" "FooD" "FooE" "FooF"
## 
## [[2]]
## [1] "Bar.py"   "Bar.bash"
## 
## [[3]]
## [1] "{{Biz}}"

glob is a wrapper around Sys.glob that uses expand_braces to support both brace and wildcard expansion on file paths.

glob("R/*.{R,r,S,s}")

## [1] "R/engine-r.R"      "R/engine-v8.R"     "R/expand_braces.R"
## [4] "R/glob.R"

Installation

To install the release version on CRAN use the following command in R:

install.packages("bracer")

To install the developmental version use the following command in R:

remotes::install_github("trevorld/bracer")

Installing the suggested V8 package will enable use of the javascript alternative parser:

install.packages("V8")

Limitations of pure R parser and alternative javascript parser

The bracer pure R parser currently does not properly support the “correct” (Bash-style) brace expansion under several edge conditions such as:

1. Unbalanced braces e.g. {{a,d} (but you could use an escaped brace instead \\{{a,d})
2. Using surrounding quotes to escape terms e.g. {'a,b','c'} (but you could use an escaped comma instead {a\\,b,c})
3. Escaped braces within comma-separated lists e.g. {a,b\\}c,d}
4. (Non-escaping) backslashes before braces e.g. {a,\\\\{a,b}c}
5. Sequences from letters to non-letter ASCII characters e.g. X{a..#}X

options(bracer.engine = "r")
expand_braces("{{a,d}")

## [1] "{{a,d}"

expand_braces("{'a,b','c'}")

## [1] "'a"  "b'"  "'c'"

expand_braces("{a,b\\}c,d}")

## [1] "a,b}c" "d"

expand_braces("{a,\\\\{a,b}c}")

## [1] "ac}"  "{ac}" "bc}"

expand_braces("X{a..#}X")

## [1] "X{a..#}X"

However if the ‘V8’ suggested R package is installed we can instead use an embedded version of the braces Javascript library which can correctly handle these edge cases. To do so we need to set the bracer “engine” to “v8”.

options(bracer.engine = "v8")
expand_braces("{{a,d}")

## [1] "{a" "{d"

expand_braces("{'a,b','c'}")

## [1] "a,b" "c"

expand_braces("{a,b\\}c,d}")

## [1] "a"   "b}c" "d"

expand_braces("{a,\\\\{a,b}c}")

## [1] "a"    "\\ac" "\\bc"

expand_braces("X{a..#}X")

##  [1] "XaX"  "X`X"  "X_X"  "X^X"  "X]X"  "X\\X" "X[X"  "XZX"  "XYX"  "XXX" 
## [11] "XWX"  "XVX"  "XUX"  "XTX"  "XSX"  "XRX"  "XQX"  "XPX"  "XOX"  "XNX" 
## [21] "XMX"  "XLX"  "XKX"  "XJX"  "XIX"  "XHX"  "XGX"  "XFX"  "XEX"  "XDX" 
## [31] "XCX"  "XBX"  "XAX"  "X@X"  "X?X"  "X>X"  "X=X"  "X<X"  "X;X"  "X:X" 
## [41] "X9X"  "X8X"  "X7X"  "X6X"  "X5X"  "X4X"  "X3X"  "X2X"  "X1X"  "X0X" 
## [51] "X/X"  "X.X"  "X-X"  "X,X"  "X+X"  "X*X"  "X)X"  "X(X"  "X'X"  "X&X" 
## [61] "X%X"  "X$X"  "X#X"