"named map builder" is an operator written as "
:=". Named map builder is a very simple bit of code that performs a very simple task: it adds names to vectors or lists (making them work more like maps).
Here are some examples:
library("wrapr") 'a' := 5 c('a' := 5, 'b' := 6) c('a', 'b') := c(5, 6)
The left-side argument of the
:= operator is called "the names", and the right-side argument is called "the values". The
:= operators returns the values with the names set to names.
:= is a left-over assignment operator in
R. It is part of the syntax, but by default not defined.
data.table has long used
:= to denote "in-place assignment" as in the following.
library("data.table") data.table(x = 1)[, y := x + 1] # x y # 1: 1 2
dplyr later adopted the
:= notation as this allows for substitution on the left-hand sides of assignments.
wrapr::qc() uses the
:= for the same purpose.
A key use of the named map builder is the following:
`:=` <- wrapr::`:=` # in case data.tables "catch calls" definition is active key = 'keycode' key := 'value'
Notice the value inside the variable
key was used as the array name, this differs from
what is easily done with
c(key = 'value') style notation.
help(`:=`, package = 'wrapr')
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