lambda Function Builder

John Mount

2020-08-10

The CRAN version of the R package wrapr package now includes a concise anonymous function constructor: l().

To use it please do the following: attach wrapr and ask it to place a definition for l() in your environment:

library("wrapr")
wrapr::defineLambda(name = "l")
ls()
##  [1] "LEFT_NAME"       "OTHER_SYMBOL"    "X"               "Y"              
##  [5] "angle"           "d"               "d2"              "df"             
##  [9] "f"               "inputs"          "l"               "plotb"          
## [13] "variable"        "variable_name"   "variable_string" "x"

Note: throughout this document we are using the letter “l” as a stand-in for the Greek letter lambda, as this non-ASCII character can cause formatting problems in some situations.

You can use l() to define functions. The syntax is: l(arg [, arg]*, body [, env=env]). That is we write a l()-call (which you can do by cutting and pasting) and list the desired function arguments and then the function body. For example the function that squares numbers is:

l(x, x^2)
## function (x) 
## x^2

We can use such a function to square the first four positive integers as follows:

sapply(1:4, l(x, x^2))
## [1]  1  4  9 16

Dot-pipe style notation does not need the l() factory as it treats pipe stages as expressions parameterized over the variable “.”:

1:4 %.>% { .^2 }
## [1]  1  4  9 16

And we can also build functions that take more than one argument as follows:

l(x, y, x + 3*y)
## function (x, y) 
## x + 3 * y