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rggplot2plotmath

including conditional elements in plotmath expression for ggplot2 subtitle

I am trying to write a custom function where I want to display an effect size estimate and its confidence intervals in ggplot2 plot subtitle. I am using plotmath to properly display Greek letters and other mathematical symbols.

This is what the two variants of the subtitle I want look like-

To achieve this, I've written a simple function- 

# set up
set.seed(123)
library(tidyverse)
library(cowplot)

# creating a fictional dataframe with effect size estimate and its confidence
# intervals
effsize_df <- tibble::tribble(
  ~estimate, ~conf.low, ~conf.high,
  0.25, 0.10, 0.40
)

# function to prepare subtitle
subtitle_maker <- function(effsize_df, effsize.type) {
  if (effsize.type == "p_eta") {
    # preparing the subtitle
    subtitle <-
      # extracting the elements of the statistical object
      base::substitute(
        expr =
          paste(
            eta["p"]^2,
            " = ",
            effsize,
            ", 95% CI",
            " [",
            LL,
            ", ",
            UL,
            "]",
          ),
        env = base::list(
          effsize = effsize_df$estimate[1],
          LL = effsize_df$conf.low[1],
          UL = effsize_df$conf.high[1]
        )
      )
  } else if (effsize.type == "p_omega") {
    # preparing the subtitle
    subtitle <-
      # extracting the elements of the statistical object
      base::substitute(
        expr =
          paste(
            omega["p"]^2,
            " = ",
            effsize,
            ", 95% CI",
            " [",
            LL,
            ", ",
            UL,
            "]",
          ),
        env = base::list(
          effsize = effsize_df$estimate[1],
          LL = effsize_df$conf.low[1],
          UL = effsize_df$conf.high[1]
        )
      )
  }

  # return the subtitle
  return(subtitle)
}

Note that the code for the conditional statements differs only on one line: eta["p"]^2 (if it's "p_eta") or omega["p"]^2 (if it's "p_omega") and the rest of the code is identical. I want to refactor this code to avoid this repetition.

I can't conditionally assign eta["p"]^2 and omega["p"]^2 to a different object in the function body (let's say effsize.text <- eta["p"]^2) because R will complain that the objects eta and omega are not found in the environment.

How can I do this?

---------------------- post-script--------------------------------------

Following is the code used to create the combined plot shown above-

# creating and joining two plots (plot is shown above)
cowplot::plot_grid(
  # plot 1
  ggplot(mtcars, aes(x = wt, y = mpg)) + geom_blank() +
    labs(
      subtitle = subtitle_maker(effsize_df, "p_omega"),
      title = "partial omega"
    ),
  # plot 2
  ggplot(mtcars, aes(x = wt, y = mpg)) + geom_blank() +
    labs(
      subtitle = subtitle_maker(effsize_df, "p_eta"),
      title = "partial eta"
    ),
  labels = c("(a)", "(b)"),
  nrow = 1
)
Solution

  • a combination of quote and bquote can help,

    subtitle_maker <- function(d, type){

  et <- if(type == 'a') quote(eta) else if(type == 'b') quote(omega)

  bquote(.(et)['p']^2==.(d$x)~", 95% CI ["*.(d$y)*","*.(d$z)*"]")

}

d <- list(x=1,y=2,z=3)
grid::grid.newpage()
grid::grid.text(subtitle_maker(d,"a"), y=0.3)
grid::grid.text(subtitle_maker(d,"b"), y=0.7)

    Note: or substitute instead of bquote, that's just personal preference

    subtitle_maker <- function(effsize_df, effsize.type) {

  effsize.text <- if (effsize.type == "p_eta") quote(eta["p"]) else 
    if (effsize.type == "p_omega") quote(omega["p"])

      base::substitute(
        expr =
          paste(effsize.text^2,
            " = ",
            effsize,
            ", 95% CI",
            " [",
            LL,
            ", ",
            UL,
            "]",
          ),
        env = base::list(effsize.text = effsize.text,
          effsize = effsize_df$estimate[1],
          LL = effsize_df$conf.low[1],
          UL = effsize_df$conf.high[1]
        )
      )
}