Title: | Define Aliases for R Expressions |
---|---|
Description: | Create aliases for other R names or arbitrarily complex R expressions. Accessing the alias acts as-if the aliased expression were invoked instead, and continuously reflects the current value of that expression: updates to the original expression will be reflected in the alias; and updates to the alias will automatically be reflected in the original expression. |
Authors: | Konrad Rudolph [cre, aut] |
Maintainer: | Konrad Rudolph <[email protected]> |
License: | MIT + file LICENSE |
Version: | 0.1.0 |
Built: | 2024-10-27 05:35:03 UTC |
Source: | https://github.com/klmr/aka |
alias(name = expr
) creates an alias for expr
named name
. Subsequently, name
can (mostly) be used interchangeably with expr
.
name %&=% expr
is the same as alias(name = expr)
.
alias(name = expr, expr_env = parent.frame(), alias_env = parent.frame()) name %=&% expr
alias(name = expr, expr_env = parent.frame(), alias_env = parent.frame()) name %=&% expr
expr_env |
the environment in which to evaluate the expression |
alias_env |
the environment in which to create the alias |
name |
the alias name |
expr |
an arbitrary R expression to be aliased by |
After executing alias(name = expr)
, name
can be used to refer to the value of expr
. This is especially useful when expr
is a complex expression that is used multiple times in the code. Unlike with regular assignment, expr
will be reevaluated every time name
is evaluated. This means that the value of name
always stays up to date, similar to a “reactive” expression. On the flip side, it also means that accessing name
can be very slow if evaluating expr
is time-consuming.
expr
can contain interpolated expressions using the bquote()
syntax (including splicing). These will be substituted at the time of defining the alias. See Examples.
The parameters expr_env
and alias_env
are used to control the environments in which the expression is evaluated and the alias is created, respectively. Note that specifying the correct expr_env
is particularly important when assigning to an alias: an expression can be evaluated inside a parent environment without having to specify expr_env
; however, during assignment this would cause the assignee object to be copied into the calling environment. See Examples for a concrete example of this.
alias()
is called for its side-effect and does not return a value.
x = 'hello' alias(ax = x) ax # prints 'hello' x = 'world' ax # prints 'world' ax = 'goodbye' x # prints 'goodbye' # Aliases can be created for complex expressions: alias(mercedes = mtcars[grepl('^Merc ', rownames(mtcars)), ]) mercedes mercedes$vs = 0 # set all Mercedes engine types to V-shaped mtcars # Aliases can contain interpolated expressions: n = 1 m = 2 alias(s = .(n) + m) s # prints 3 n = 10 m = 10 s # prints 11 alias_expr('s') # prints `1 + m` # Be careful when assigning to an alias to an object in a parent environment: e = attach(new.env()) e$y = 'hello' alias(ay = y) # Works: `y` is found in the parent environment ay # prints 'hello' # But the following creates a *new variable* `y` in the current environment: ay = 'world' e$y # prints 'hello', still! y # prints 'world' # To prevent this, use `expr_env`: # alias(ay = y, expr_env = e)
x = 'hello' alias(ax = x) ax # prints 'hello' x = 'world' ax # prints 'world' ax = 'goodbye' x # prints 'goodbye' # Aliases can be created for complex expressions: alias(mercedes = mtcars[grepl('^Merc ', rownames(mtcars)), ]) mercedes mercedes$vs = 0 # set all Mercedes engine types to V-shaped mtcars # Aliases can contain interpolated expressions: n = 1 m = 2 alias(s = .(n) + m) s # prints 3 n = 10 m = 10 s # prints 11 alias_expr('s') # prints `1 + m` # Be careful when assigning to an alias to an object in a parent environment: e = attach(new.env()) e$y = 'hello' alias(ay = y) # Works: `y` is found in the parent environment ay # prints 'hello' # But the following creates a *new variable* `y` in the current environment: ay = 'world' e$y # prints 'hello', still! y # prints 'world' # To prevent this, use `expr_env`: # alias(ay = y, expr_env = e)
alias_expr(alias)
returns the expression that was used to define an alias.
alias_env(alias)
returns the environment in which the aliased expression is evaluated.
alias_expr(alias, envir = parent.frame()) alias_env(alias, envir = parent.frame())
alias_expr(alias, envir = parent.frame()) alias_env(alias, envir = parent.frame())
alias |
the name of an alias, as a string |
envir |
the environment in which to look up the alias name (default: calling environment) |
alias_expr(alias)
returns an unevaluated R expression (a name or a call).
alias_env(alias)
returns an environment.