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Wrap a function to capture errors

Source: R/adverb-safely.R
safely.Rd

Creates a modified version of .f that always succeeds. It returns a list with components result and error. If the function succeeds, result contains the returned value and error is NULL. If an error occurred, error is an error object and result is either NULL or otherwise.

Usage

safely(.f, otherwise = NULL, quiet = TRUE)

Arguments

.f

A function to modify, specified in one of the following ways:

  • A named function, e.g. mean.

  • An anonymous function, e.g. \(x) x + 1 or function(x) x + 1.

  • A formula, e.g. ~ .x + 1. Only recommended if you require backward compatibility with older versions of R.

otherwise

Default value to use when an error occurs.

quiet

Hide errors (TRUE, the default), or display them as they occur?

Value

A function that takes the same arguments as .f, but returns a different value, as described above.

Adverbs

This function is called an adverb because it modifies the effect of a function (a verb). If you'd like to include a function created an adverb in a package, be sure to read faq-adverbs-export.

See also

Other adverbs: auto_browse(), compose(), insistently(), negate(), partial(), possibly(), quietly(), slowly()

Examples

safe_log <- safely(log)
safe_log(10)
#> $result
#> [1] 2.302585
#> 
#> $error
#> NULL
#> 
safe_log("a")
#> $result
#> NULL
#> 
#> $error
#> <simpleError in .Primitive("log")(x, base): non-numeric argument to mathematical function>
#> 

list("a", 10, 100) |>
  map(safe_log) |>
  transpose()
#> $result
#> $result[[1]]
#> NULL
#> 
#> $result[[2]]
#> [1] 2.302585
#> 
#> $result[[3]]
#> [1] 4.60517
#> 
#> 
#> $error
#> $error[[1]]
#> <simpleError in .Primitive("log")(x, base): non-numeric argument to mathematical function>
#> 
#> $error[[2]]
#> NULL
#> 
#> $error[[3]]
#> NULL
#> 
#> 

# This is a bit easier to work with if you supply a default value
# of the same type and use the simplify argument to transpose():
safe_log <- safely(log, otherwise = NA_real_)
list("a", 10, 100) |>
  map(safe_log) |>
  transpose() |>
  simplify_all()
#> $result
#> [1]       NA 2.302585 4.605170
#> 
#> $error
#> $error[[1]]
#> <simpleError in .Primitive("log")(x, base): non-numeric argument to mathematical function>
#> 
#> $error[[2]]
#> NULL
#> 
#> $error[[3]]
#> NULL
#> 
#>