flextable: embed ggpplots using data from 2 columns with lists (for comparing) as a single plot per row

Question

Following https://ardata-fr.github.io/flextable-book/cell-content-1.html#base-plots-and-ggplot-objects I would like to have small plots.

   gg_line <- function(z) {
  z <- scale(z)
  z <- na.omit(z)
  z <- data.frame(x = seq_along(z), z = z)
  ggplot(z, aes(x = x, y = z)) +
    geom_line(show.legend = FALSE) +
    theme_void()
}

Build a dataset, embed a list with data.

  dat <- as.data.table(mtcars)
z <- dat[,
         lapply(.SD, function(x) list(gg_line(x))),
         by = c("vs", "am"), .SDcols = c("mpg", "disp")
]

Replace ggplot data in cells with plots.

  ft <- flextable(z)
ft <- compose(ft, 
              j = c("mpg", "disp", "drat"),
              value = as_paragraph(gg_chunk(value = ., height = .15, width = 1)),
              use_dot = TRUE
)
ft

As a result I have 2 columns with plots.

I am wondering how to change the code so that instead of two columns one is produced: one ggplot per row with superimposed two geoms (in this case for "mpg" and "disp" but this could be two groups present in the dataset like two companies, two species). I wish I could plot side by side in each cell two boxplots or two violin plots in one cell. Is there an easy way to combine two lists, from two columns, to generate one column with a single plot per each record that shows data from two lists (two layers)?

Answer 1

Unfortunately I lack the data.table skills to do the data wrangling via data.table but making use of the tidyverse this could be achieved like so:

library(flextable)
library(ggplot2)
library(tidyr)
library(dplyr)

gg <- function(z, cols, type = "box") {
  z <- z[, cols]
  z <- dplyr::mutate(z, dplyr::across(all_of(cols), scale), x = seq(nrow(z)))
  z <- na.omit(z)
  z <- tidyr::pivot_longer(z, -x)
  
  geom <- switch(type,
                 line = geom_line(aes(x = x), show.legend = FALSE),
                 box = geom_boxplot(aes(x = name), show.legend = FALSE, size = .1))
  ggplot(z, aes(y = value, color = name)) +
    geom +
    theme_void()
}

dat <- mtcars
dat <- dat %>% 
  tidyr::nest(data = -c(vs, am)) %>% 
  dplyr::mutate(
    line = lapply(data, function(x) gg(x, cols = c("mpg", "disp"), "line")),
    box = lapply(data, function(x) gg(x, cols = c("mpg", "disp"), "box"))) %>% 
  dplyr::select(-data)

ft <- flextable(dat[, c("vs", "am", "line")])
ft <- compose(ft, 
              j = c("line"),
              value = as_paragraph(gg_chunk(value = ., height = .15, width = 1)),
              use_dot = TRUE
)
ft

ft <- flextable(dat[, c("vs", "am", "box")])
ft <- compose(ft, 
              j = c("box"),
              value = as_paragraph(gg_chunk(value = ., height = .15, width = 1)),
              use_dot = TRUE
)
ft