Parse Trellis formula

Description

this function is used by high level Lattice functions like xyplot to parse the formula argument and evaluate various components of the data.

Usage

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latticeParseFormula(model, data, dimension = 2,
                    subset = TRUE, groups = NULL,
                    multiple, outer,
                    subscripts,
                    drop)

Arguments

model

the model/formula to be parsed. This can be in either of two possible forms, one for 2d and one for 3d formulas, determined by the dimension argument. The 2d formulas are of the form y ~ x| g1 * ... *gn, and the 3d formulas are of the form z ~ x * y | g1 * ...* gn. In the first form, y may be omitted. The conditioning variables g1, ...,gn can be omitted in either case.

data

the environment/dataset where the variables in the formula are evaluated.

dimension

dimension of the model, see above

subset

index for choosing a subset of the data frame

groups

the grouping variable, if present

multiple, outer

logicals, determining how a ‘+’ in the y and x components of the formula are processed. See xyplot for details

subscripts

logical, whether subscripts are to be calculated

drop

logical or list, similar to the drop.unused.levels argument in xyplot, indicating whether unused levels of conditioning factors and data variables that are factors are to be dropped.

Value

returns a list with several components, including left, right, left.name, right.name, condition for 2-D, and left, right.x, right.y, left.name, right.x.name, right.y.name, condition for 3-D. Other possible components are groups, subscr

Author(s)

Saikat DebRoy, Deepayan Sarkar Deepayan.Sarkar@R-project.org

See Also

xyplot, Lattice

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