Get or set observations in a vector
This provides a common interface to extracting and modifying observations
for all vector types, regardless of dimensionality. It is an analog to [
that matches vec_size() instead of length().
vec_slice(x, i) vec_slice(x, i) <- value vec_assign(x, i, value, ..., x_arg = "", value_arg = "")
x |
A vector |
i |
An integer, character or logical vector specifying the
locations or names of the observations to get/set. Specify
|
value |
Replacement values. |
... |
These dots are for future extensions and must be empty. |
x_arg, value_arg |
Argument names for |
A vector of the same type as x.
Support for S3 objects depends on whether the object implements a
vec_proxy() method.
When a vec_proxy() method exists, the proxy is sliced and
vec_restore() is called on the result.
Otherwise vec_slice() falls back to the base generic [.
Note that S3 lists are treated as scalars by default, and will
cause an error if they don't implement a vec_proxy() method.
vec_slice() only slices along one dimension. For
two-dimensional types, the first dimension is subsetted.
vec_slice() preserves attributes by default.
vec_slice<-() is type-stable and always returns the same type
as the LHS.
base::`[`
If a non-data-frame vector class doesn't have a vec_proxy()
method, the vector is sliced with [ instead.
x <- sample(10) x vec_slice(x, 1:3) # You can assign with the infix variant: vec_slice(x, 2) <- 100 x # Or with the regular variant that doesn't modify the original input: y <- vec_assign(x, 3, 500) y x # Slicing objects of higher dimension: vec_slice(mtcars, 1:3) # Type stability -------------------------------------------------- # The assign variant is type stable. It always returns the same # type as the input. x <- 1:5 vec_slice(x, 2) <- 20.0 # `x` is still an integer vector because the RHS was cast to the # type of the LHS: vec_ptype(x) # Compare to `[<-`: x[2] <- 20.0 vec_ptype(x) # Note that the types must be coercible for the cast to happen. # For instance, you can cast a double vector of whole numbers to an # integer vector: vec_cast(1, integer()) # But not fractional doubles: try(vec_cast(1.5, integer())) # For this reason you can't assign fractional values in an integer # vector: x <- 1:3 try(vec_slice(x, 2) <- 1.5)
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