A simple density plot generator

readme.md

A function to generate simple density plots.

Example

Single density plots can be generated:

(
  density_plot(
      test_1_data,
      x = "grade",
      title = "Density of Grades",
      limits = c(0, 100)
  )
  + labs(x = "Grade (/100)")
)

Or plots can be wrapped by proviging a group_on argument:

(
  density_plot(
      test_1_data,
      x = "grade",
      title = "Density of Grades By Stream",
      group_on = "stream",
      limits = c(0, 100)
  )
  + labs(x = "Grade (/100)")
)

density_plot.R

library(tidyverse)

#' Returns a beautiful density plot
#'
#' @param data A data frame
#' @param x The x-axis variable as a string
#' @param group_on (optional) The variable to facet-wrap on as a string
#' @param title (optional) The title, if given will append "(n=<n>)"
#' @param limits (optional) a numeric vector of length 2 specifying the min and max values
#' @returns A ggplot2 plot
density_plot <- function(
        data,
        x,
        title = NULL,
        group_on = NULL,
        limits = NULL
) {
    plot <- ggplot(data, aes(x = !!as.name(x)))

    if (!is.null(group_on)) {
        data <- data |> group_by(!!as.name(group_on))
    }

    summary <- (
        data
        |> summarise(
               mean = mean(!!as.name(x)),
               median = median(!!as.name(x)),
               n = n()
           )
    )

    if (!is.null(group_on)) {
        plot <- plot + facet_wrap(
            ~ get(group_on),
            dir = "v",
            labeller = as_labeller(~ paste0(
                .x,
                " (n=",
                (summary |> filter(!!as.name(group_on) == .x) |> pull(n)),
                ")"
            ))
        )
    }

    if (!is.null(title)) {
        total <- summary |> pull(n) |> sum()
        plot <- plot + labs(title = paste0(title, " (n=", total, ")"))
    }

    return(
        plot
        + geom_density(alpha = 0.25, fill = "salmon")
        + theme(plot.title = element_text(face = "bold"))
        + scale_x_continuous(expand = expansion(add = 1.05), limits = limits)
        + scale_colour_manual(
              name = "Summary", values = c(mean = "red", median = "blue")
          )
        + scale_linetype_manual(
              name = "Summary", values = c(mean = "solid", median = "longdash")
          )
        + geom_vline(
              aes(xintercept = mean, color = "mean", linetype = "mean"),
              data = summary
          )
        + geom_vline(
              aes(xintercept = median, color = "median", linetype = "median"),
              data = summary
          )
        + labs(color = "Summary", linetype = "Summary")
    )
}

density_plot_grid.R

#' Returns a beautiful 2x2 density plot grid
#'
#' @param data A data frame
#' @param x The x-axis variable as a string
#' @param group_on A character vector of exactly two variables to use as the
#'  rows and columns of the grid in that order
#' @param x_limits A numeric vector of length 2 specifying the min and max values for the x-axis
#' @param title The title — The number of observations will be appended "(n=<n>)"
#' @param scales (optional) scales used in facet wrap (if group_on is provided)
#' @returns A ggplot2 plot
density_grid <- function(
        data,
        x,
        group_on,
        x_limits,
        title,
        scales = "fixed"
) {
    data <- data |> group_by(!!as.name(group_on[1]), !!as.name(group_on[2]))
    summary <- (
        data
        |> summarise(
            mean = mean(!!as.name(x)),
            median = median(!!as.name(x)),
            n = n(),
            .groups = "keep"
        )
    )

    total <- summary |> pull(n) |> sum()

    label_x_position = x_limits[1] + 0.1 * (x_limits[2] - x_limits[1])
    max_y <- (
        data
        |> reframe(density = max(density(!!as.name(x))$y))
        |> pull(density)
        |> max()
    )

    return(
        ggplot(data, aes(x = !!as.name(x)))
        + geom_density(alpha = 0.25, fill = "salmon")
        + facet_grid(
            rows = vars(!!as.name(group_on[1])),
            cols = vars(!!as.name(group_on[2]))
          )
        + geom_text(
            data = summary,
            aes(x = label_x_position, y = max_y * 0.975, label = paste0("n=", n)),
            inherit.aes = FALSE,
            parse = FALSE
          )
        + theme(plot.title = element_text(face = "bold"))
        + scale_x_continuous(expand = expansion(add = 1.05), limits = x_limits)
        + scale_colour_manual(
            name = "Summary",
            values = c(mean = "red", median = "blue")
          )
        + scale_linetype_manual(
            name = "Summary",
            values = c(mean = "solid", median = "longdash")
          )
        + geom_vline(
            aes(xintercept = mean, color = "mean", linetype = "mean"),
            data = summary
          )
        + geom_vline(
            aes(xintercept = median, color = "median", linetype = "median"),
            data = summary
          )
        + labs(
            title = paste0(title, " (n=", total, ")"),
            color = "Summary",
            linetype = "Summary"
          )
        + theme(panel.spacing.x = unit(0.75, "lines"))
    )
}