faq-compatibility-types: FAQ - How is the compatibility of vector types decided?

Description Common type of multiple vectors Type conversion and lossy cast errors How to make two vector classes compatible?

Description

Two vectors are compatible when you can safely:

Examples of compatible types are integer and double vectors. On the other hand, integer and character vectors are not compatible.

Common type of multiple vectors

There are two possible outcomes when multiple vectors of different types are combined into a larger vector:

In general, the common type is the richer type, in other words the type that can represent the most values. Logical vectors are at the bottom of the hierarchy of numeric types because they can only represent two values (not counting missing values). Then come integer vectors, and then doubles. Here is the vctrs type hierarchy for the fundamental vectors:

coerce.png

Type conversion and lossy cast errors

Type compatibility does not necessarily mean that you can convert one type to the other type. That’s because one of the types might support a larger set of possible values. For instance, integer and double vectors are compatible, but double vectors can’t be converted to integer if they contain fractional values.

When vctrs can’t convert a vector because the target type is not as rich as the source type, it throws a lossy cast error. Assigning a fractional number to an integer vector is a typical example of a lossy cast error:

int_vector <- 1:3
vec_assign(int_vector, 2, 0.001)
#> Error: Can't convert from <double> to <integer> due to loss of precision.
#> * Locations: 1

How to make two vector classes compatible?

If you encounter two vector types that you think should be compatible, they might need to implement coercion methods. Reach out to the author(s) of the classes and ask them if it makes sense for their classes to be compatible.

These developer FAQ items provide guides for implementing coercion methods:


vctrs documentation built on April 29, 2021, 5:08 p.m.