Cast a vector to a specified type

vec_cast() provides directional conversions from one type of vector to another. Along with vec_ptype2(), this generic forms the foundation of type coercions in vctrs.

vec_cast(x, to, ..., x_arg = "", to_arg = "")

vec_cast_common(..., .to = NULL)

# S3 method for logical
vec_cast(x, to, ...)

# S3 method for integer
vec_cast(x, to, ...)

# S3 method for double
vec_cast(x, to, ...)

# S3 method for complex
vec_cast(x, to, ...)

# S3 method for raw
vec_cast(x, to, ...)

# S3 method for character
vec_cast(x, to, ...)

# S3 method for list
vec_cast(x, to, ...)

Arguments

x	Vectors to cast.
to, .to	Type to cast to. If `NULL`, `x` will be returned as is.
...	For `vec_cast_common()`, vectors to cast. For `vec_cast()`, `vec_cast_default()`, and `vec_restore()`, these dots are only for future extensions and should be empty.
x_arg, to_arg	Argument names for `x` and `to`. These are used in error messages to inform the user about the locations of incompatible types (see `stop_incompatible_type()`).

Value

A vector the same length as x with the same type as to, or an error if the cast is not possible. An error is generated if information is lost when casting between compatible types (i.e. when there is no 1-to-1 mapping for a specific value).

Implementing coercion methods

For an overview of how these generics work and their roles in vctrs, see ?theory-faq-coercion.
For an example of implementing coercion methods for simple vectors, see ?howto-faq-coercion.
For an example of implementing coercion methods for data frame subclasses, see ?howto-faq-coercion-data-frame.
For a tutorial about implementing vctrs classes from scratch, see vignette("s3-vector").

Dependencies of `vec_cast_common()`

vctrs dependencies

vec_ptype2()
vec_cast()

base dependencies

Some functions enable a base-class fallback for vec_cast_common(). In that case the inputs are deemed compatible when they have the same base type and inherit from the same base class.

Examples

# x is a double, but no information is lost
vec_cast(1, integer())
#> [1] 1

# When information is lost the cast fails
try(vec_cast(c(1, 1.5), integer()))
#> Error : Can't convert from <double> to <integer> due to loss of precision.
#> • Locations: 2
try(vec_cast(c(1, 2), logical()))
#> Error : Can't convert from <double> to <logical> due to loss of precision.
#> • Locations: 2

# You can suppress this error and get the partial results
allow_lossy_cast(vec_cast(c(1, 1.5), integer()))
#> [1] 1 1
allow_lossy_cast(vec_cast(c(1, 2), logical()))
#> [1] TRUE TRUE

# By default this suppress all lossy cast errors without
# distinction, but you can be specific about what cast is allowed
# by supplying prototypes
allow_lossy_cast(vec_cast(c(1, 1.5), integer()), to_ptype = integer())
#> [1] 1 1
try(allow_lossy_cast(vec_cast(c(1, 2), logical()), to_ptype = integer()))
#> Error : Can't convert from <double> to <logical> due to loss of precision.
#> • Locations: 2

# No sensible coercion is possible so an error is generated
try(vec_cast(1.5, factor("a")))
#> Error : Can't convert <double> to <factor<4d52a>>.

# Cast to common type
vec_cast_common(factor("a"), factor(c("a", "b")))
#> [[1]]
#> [1] a
#> Levels: a b
#> 
#> [[2]]
#> [1] a b
#> Levels: a b
#>