Define aesthetic mappings programatically

Aesthetic mappings describe how variables in the data are mapped to visual properties (aesthetics) of geoms. aes uses non-standard evaluation to capture the variable names. aes_ and aes_string require you to explicitly quote the inputs either with "" for aes_string(), or with quote or ~ for aes_(). (aes_q is an alias to aes_). This makes aes_ and aes_string easy to program with.

aes_(x, y, ...)

aes_string(x, y, ...)

aes_q(x, y, ...)

Arguments

x, y, ...	List of name value pairs. Elements must be either quoted calls, strings, one-sided formulas or constants.

Details

aes_string and aes_ are particularly useful when writing functions that create plots because you can use strings or quoted names/calls to define the aesthetic mappings, rather than having to use substitute to generate a call to aes().

I recommend using aes_(), because creating the equivalents of aes(colour = "my colour") or aes{x = `X$1`} with aes_string() is quite clunky.

See also

aes

Examples

# Three ways of generating the same aesthetics
aes(mpg, wt, col = cyl)
#> * x      -> mpg
#> * y      -> wt
#> * colour -> cyl
aes_(quote(mpg), quote(wt), col = quote(cyl))
#> * colour -> cyl
#> * x      -> mpg
#> * y      -> wt
aes_(~mpg, ~wt, col = ~cyl)
#> * colour -> cyl
#> * x      -> mpg
#> * y      -> wt
aes_string("mpg", "wt", col = "cyl")
#> * colour -> cyl
#> * x      -> mpg
#> * y      -> wt

# You can't easily mimic these calls with aes_string
aes(`$100`, colour = "smooth")
#> * x      -> `$100`
#> * colour -> "smooth"
aes_(~ `$100`, colour = "smooth")
#> * colour -> "smooth"
#> * x      -> `$100`
# Ok, you can, but it requires a _lot_ of quotes
aes_string("`$100`", colour = '"smooth"')
#> * colour -> "smooth"
#> * x      -> `$100`

# Convert strings to names with as.name
var <- "cyl"
aes(col = x)
#> * colour -> x
aes_(col = as.name(var))
#> * colour -> cyl