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Create a symbol or list of symbols

Source: R/sym.R
sym.Rd

Symbols are a kind of defused expression that represent objects in environments.

  • sym() and syms() take strings as input and turn them into symbols.

  • data_sym() and data_syms() create calls of the form .data$foo instead of symbols. Subsetting the .data pronoun is more robust when you expect a data-variable. See The data mask ambiguity.

Only tidy eval APIs support the .data pronoun. With base R functions, use simple symbols created with sym() or syms().

Usage

sym(x)

syms(x)

data_sym(x)

data_syms(x)

Arguments

x

For sym() and data_sym(), a string. For syms() and data_syms(), a list of strings.

Value

For sym() and syms(), a symbol or list of symbols. For data_sym() and data_syms(), calls of the form .data$foo.

See also

Examples

# Create a symbol
sym("cyl")
#> cyl

# Create a list of symbols
syms(c("cyl", "am"))
#> [[1]]
#> cyl
#> 
#> [[2]]
#> am
#> 

# Symbolised names refer to variables
eval(sym("cyl"), mtcars)
#>  [1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4

# Beware of scoping issues
Cyl <- "wrong"
eval(sym("Cyl"), mtcars)
#> [1] "wrong"

# Data symbols are explicitly scoped in the data mask
try(eval_tidy(data_sym("Cyl"), mtcars))
#> Error in .data$Cyl : Column `Cyl` not found in `.data`.

# These can only be used with tidy eval functions
try(eval(data_sym("Cyl"), mtcars))
#> Error in eval(data_sym("Cyl"), mtcars) : 
#>   Can't subset `.data` outside of a data mask context.

# The empty string returns the missing argument:
sym("")
#> 

# This way sym() and as_string() are inverse of each other:
as_string(missing_arg())
#> [1] ""
sym(as_string(missing_arg()))
#>