emmeans (version 1.3.2)

add_grouping: Add a grouping factor

Description

This function adds a grouping factor to an existing reference grid or other emmGrid object, such that the levels of an existing factor (call it the reference factor) are mapped to a smaller number of levels of the new grouping factor. The reference factor is then nested in the grouping factor. This facilitates obtaining marginal means of the grouping factor, and contrasts thereof.

Usage

add_grouping(object, newname, refname, newlevs)

Arguments

object

An emmGrid object

newname

Character name of grouping factor to add (different from any existing factor in the grid)

refname

Character name of the reference factor

newlevs

Character vector or factor of the same length as that of the levels for refname. The grouping factor newname will have the unique values of newlevs as its levels.

Value

A revised emmGrid object having an additional factor named newname, and a new nesting structure refname %in% newname

Examples

# NOT RUN {
fiber.lm <- lm(strength ~ diameter + machine, data = fiber)
( frg <- ref_grid(fiber.lm) )

# Suppose the machines are two different brands
brands <- factor(c("FiberPro", "FiberPro", "Acme"), levels = c("FiberPro", "Acme"))
( gfrg <- add_grouping(frg, "brand", "machine", brands) )

emmeans(gfrg, "machine")

emmeans(gfrg, "brand")
# }

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