Coerce into a Covariance Structure Definition

Usage

as.cov_struct(x, ...)

# S3 method for class 'formula'
as.cov_struct(x, warn_partial = TRUE, ...)

Arguments

x: an object from which to derive a covariance structure. See object specific sections for details.
...: additional arguments unused.
warn_partial: (flag)
whether to emit a warning when parts of the formula are disregarded.

Value

A cov_struct() object.

Details

A covariance structure can be parsed from a model definition formula or call. Generally, covariance structures defined using non-standard evaluation take the following form:

type( (visit, )* visit | (group /)? subject )

For example, formulas may include terms such as

us(time | subject)
cp(time | group / subject)
sp_exp(coord1, coord2 | group / subject)

Note that only sp_exp (spatial) covariance structures may provide multiple coordinates, which identify the Euclidean distance between the time points.

Methods (by class)

as.cov_struct(formula): When provided a formula, any specialized functions are assumed to be covariance structure definitions and must follow the form:
```
y ~ xs + type( (visit, )* visit | (group /)? subject )
```
Any component on the right hand side of a formula is considered when searching for a covariance definition.

Examples

# provide a covariance structure as a right-sided formula
as.cov_struct(~ csh(visit | group / subject))
#> <covariance structure>
#> heterogeneous compound symmetry:
#> 
#>   visit | group / subject
#>  

# when part of a full formula, suppress warnings using `warn_partial = FALSE`
as.cov_struct(y ~ x + csh(visit | group / subject), warn_partial = FALSE)
#> <covariance structure>
#> heterogeneous compound symmetry:
#> 
#>   visit | group / subject
#>