Combining plots with combine_plots

ggstatsplot contains a “helper” function named combine_plots to help you combine several plots into one plot or add a combination of title, caption, and annotation texts with suitable default parameters. It is a wrapper around cowplot::plot_grid(). Some examples below.

Note Before: If you have just one grouping variable and you’d like a plot for each factor of this variable the grouped_ variants (https://indrajeetpatil.github.io/ggstatsplot/reference/index.html) of all ggstatsplot functions will allow you do to this. They specifically use the combine_plots function under the covers.

Combining multiple plots: Example #1 using purrr

The full power of ggstatsplot can be leveraged with a functional programming package like purrr which can replace many for loops, is more succinct, and easier to read. Consider purrr as your first choice for combining multiple plots.

An example using the iris dataset is provided below. Imagine that we want to separately plot the linear relationship between sepal length and sepal width for each of the three species but combine them into one consistent plot with common labeling and as one plot. Rather than call ggscatterstats three times and gluing the results or using cowplot directly, we’ll create a tibble called plots using purrr::map then feed that to combine_plots to get our combined plot.

library(ggstatsplot)

# for reproducibility
set.seed(123)

# creating a list column with `ggstatsplot` plots
plots <- datasets::iris %>%
  dplyr::mutate(.data = ., Species2 = Species) %>% # just creates a copy of this variable
  dplyr::group_by(.data = ., Species) %>%                
  tidyr::nest(data = .) %>%                        # a nested dataframe with list column called `data`
  dplyr::mutate(                                   # creating a new list column of ggstatsplot outputs
    .data = .,
    plot = data %>%
      purrr::map(
        .x = .,
        .f = ~ ggstatsplot::ggscatterstats(
          data = .,
          x = Sepal.Length,
          y = Sepal.Width,
          xfill = "#0072B2",
          yfill = "#009E73",
          ggtheme = ggthemes::theme_fivethirtyeight(),
          ggstatsplot.layer = FALSE,
          messages = FALSE,                        # turns off warnings and notes messages   
          marginal.type = "boxplot",
          title =
            glue::glue("Species: {.$Species2} (n = {length(.$Sepal.Length)})")
        )
      )
  )

# display the new object (notice that the class of the `plot` list column is
# S3: ggExtraPlot)
plots
#> # A tibble: 3 x 3
#>   Species    data              plot             
#>   <fct>      <list>            <list>           
#> 1 setosa     <tibble [50 x 5]> <S3: ggExtraPlot>
#> 2 versicolor <tibble [50 x 5]> <S3: ggExtraPlot>
#> 3 virginica  <tibble [50 x 5]> <S3: ggExtraPlot>

# creating a grid with cowplot
ggstatsplot::combine_plots(
  plotlist = plots$plot,                           # list column containing all ggstatsplot objects
  nrow = 3,
  ncol = 1,
  title.text = "Relationship between sepal length and width for each Iris species",
  title.size = 14,
  caption.text = expression(
    paste(
      italic("Note"),
      ": Iris flower dataset was collected by Edgar Anderson.",
      sep = ""
    ),
    caption.size = 12
  )
)

Combining multiple plots: Example #2 with plyr

Another popular package for handling big datasets is plyr, which allows us to repeatedly apply a common function on smaller pieces and then combine the results into a larger whole.

In this example we’ll start with the gapminder dataset. We’re interested in the linear relationship between Gross Domestic Product (per capita) and life expectancy in the year 2007, for all the continents except Oceania. We’ll use dplyr to filter to the right rows then use plyr to repeat the ggscatterstats function across each of the 4 continents remaining. The result is of that is a list of plots called plots. We then feed plots to the combine_plots function to merge them into one plot. We will call attention to the countries which have very low life expectancy (< 45 years) by labeling those countries when they occur.

Adding additional textual information: Example #3

The combine_plots function can also be useful for adding additional textual information that can not be added by making a single call to a ggstatsplot function via the title, subtitle, or caption options. For this example let’s assume we want to assess the relationship between a movie’s rating and its budget from the Internet Movie Database using polynomial regression.

ggcoefstats will do most of the work, including the title, subtitle, and caption. But we want to add at the bottom an annotation to show the formula we are using for our regression. combine_plots allows us to add sub.text = to accomplish that task as shown in the resulting plot.

Suggestions

If you find any bugs or have any suggestions/remarks, please file an issue on GitHub: https://github.com/IndrajeetPatil/ggstatsplot/issues