R/interaction_plot.R

In hojsgaard/doBy: Groupwise Statistics, LSmeans, Linear Estimates, Utilities

#' @title Two-way interaction plot 
#'
#' @description Plots the mean of the response for
#'     two-way combinations of factors, thereby illustrating possible
#'     interactions.
#'
#' @name interaction-plot
#'
#' @note This is a recent addition to the package and is subject to change.
#'
#' @param .data A data frame
#' @param .formula A formula of the form `y ~ x1 + x2`
#' @param interval Either `conf.int`, `boxplot` or `none`
#'
#' @examples
#'
#' ToothGrowth |> interaction_plot(len ~ dose + supp)
#' ToothGrowth |> interaction_plot(len ~ dose + supp, interval="conf.int")
#' ToothGrowth |> interaction_plot(len ~ dose + supp, interval="boxplot")
#' ToothGrowth |> interaction_plot(len ~ dose + supp, interval="none")

#' @import dplyr
#' @import ggplot2

#' @export
interaction_plot <- function(.data, .formula, interval="conf.int"){

    interval = match.arg(tolower(interval), c("conf.int", "boxplot", "none"))

    if (!inherits(.formula, "formula")) stop("'.formula' is not formula")
    if (length(.formula) != 3)          stop("'.formula' is not two sided")
    
    lhs <- all.vars(.formula[[2]])
    rhs <- all.vars(.formula[[3]])
    if (length(rhs) < 2) stop("rhs must have at least two elements")

    rr <- sym(lhs)
    s1 <- sym(rhs[1])
    s2 <- sym(rhs[2])
    
    ## If lhs is transformed
    resp <- eval(.formula[[2]], .data)
    .data$RESP <- resp  ## KLUDGY
    rr2 <- sym("RESP")  ## KLUDGY

    dd1 <- .data |> group_by(!!sym(s1), !!sym(s2)) 
    tmp <- dd1 |> summarise(val = mean({{ rr2 }}),
                             sd  = sd({{ rr2 }}) / sqrt(n()),
                             lwr = .data$val - 1.96 * sd, upr=.data$val + 1.96 * sd,
                             .groups="keep")
    ##print(.data); print(dd1); print(tmp)

    switch(interval,
           "boxplot" = {
               ## BOXPLOT
               pp <- ggplot(.data, aes(x = factor(!!sym(s1)), y = !!sym(rr2),
                                       colour = !!sym(s2))) 
               
               pp + labs(y = deparse(.formula[[2]]), x=rhs[1]) +
                   geom_boxplot() + ## FIXME want conf. interval bars
                   geom_point(data = tmp, aes(y = .data$val)) +
                   geom_line(data = tmp, aes(y = .data$val, group = !!sym(s2))) + 
                   theme_bw()
           },
           "conf.int" = {
               ## mean +/- 2 sd
               pp <- ggplot(tmp, aes(x = factor(!!sym(s1)), y = .data$val,
                                     colour = !!sym(s2)))
               
               pp + labs(y = deparse(.formula[[2]]), x=rhs[1]) +
                   geom_point(data = tmp, aes(y = .data$val)) +
                   geom_line(data = tmp, aes(y = .data$val, group = !!sym(s2))) + 
                   geom_errorbar(aes(ymin=.data$lwr, ymax=.data$upr), data=tmp,
                                 width=.4, position=position_dodge(0.1))
           },
           "none" = {
               pp <- ggplot(tmp, aes(x = factor(!!sym(s1)), y = .data$val,
                                     colour = !!sym(s2)))               
               pp + labs(y = deparse(.formula[[2]]), x=rhs[1]) + 
                   geom_point(data = tmp, aes(y = .data$val)) +
                   geom_line(data = tmp, aes(y = .data$val, group = !!sym(s2))) 
           })
}