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).
Usage
alias(name = expr, expr_env = parent.frame(), alias_env = parent.frame())
name %=&% exprDetails
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.
Examples
x = 'hello'
alias(ax = x)
ax # prints 'hello'
#> [1] "hello"
x = 'world'
ax # prints 'world'
#> [1] "world"
ax = 'goodbye'
x # prints 'goodbye'
#> [1] "goodbye"
# Aliases can be created for complex expressions:
alias(mercedes = mtcars[grepl('^Merc ', rownames(mtcars)), ])
mercedes
#> mpg cyl disp hp drat wt qsec vs am gear carb
#> Merc 240D 24.4 4 146.7 62 3.69 3.19 20.0 1 0 4 2
#> Merc 230 22.8 4 140.8 95 3.92 3.15 22.9 1 0 4 2
#> Merc 280 19.2 6 167.6 123 3.92 3.44 18.3 1 0 4 4
#> Merc 280C 17.8 6 167.6 123 3.92 3.44 18.9 1 0 4 4
#> Merc 450SE 16.4 8 275.8 180 3.07 4.07 17.4 0 0 3 3
#> Merc 450SL 17.3 8 275.8 180 3.07 3.73 17.6 0 0 3 3
#> Merc 450SLC 15.2 8 275.8 180 3.07 3.78 18.0 0 0 3 3
mercedes$vs = 0 # set all Mercedes engine types to V-shaped
mtcars
#> mpg cyl disp hp drat wt qsec vs am gear carb
#> Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
#> Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
#> Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
#> Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
#> Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
#> Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
#> Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
#> Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 0 0 4 2
#> Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 0 0 4 2
#> Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 0 0 4 4
#> Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 0 0 4 4
#> Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
#> Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
#> Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
#> Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
#> Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
#> Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
#> Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
#> Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
#> Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
#> Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
#> Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
#> AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2
#> Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4
#> Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
#> Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
#> Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
#> Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
#> Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
#> Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
#> Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
#> Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
# Aliases can contain interpolated expressions:
n = 1
m = 2
alias(s = .(n) + m)
s # prints 3
#> [1] 3
n = 10
m = 10
s # prints 11
#> [1] 11
alias_expr('s') # prints `1 + m`
#> 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'
#> [1] "hello"
# But the following creates a *new variable* `y` in the current environment:
ay = 'world'
e$y # prints 'hello', still!
#> [1] "hello"
y # prints 'world'
#> [1] "world"
# To prevent this, use `expr_env`:
# alias(ay = y, expr_env = e)