knitr::opts_chunk$set( collapse = TRUE, comment = "#>" )
ggstatsplot::ggscatterstats is meant to provide a
publication-ready scatterplot with all statistical details included in the
plot itself to show association between two continuous variables. This function
is also helpful during the data exploration phase. We will see examples of how
to use this function in this vignette with the
To begin with, here are some instances where you would want to use
- to check linear association between two continuous variables
- to check distribution of two continuous variables
Note before: The following demo uses the pipe operator (
%>%), so in case
you are not familiar with this operator, here is a good explanation:
Correlation plot with
To illustrate how this function can be used, we will rely on the
dataset. This dataset provides information about movies scraped from
IMDB. Specifically, we will be using cleaned version of
this dataset included in the
ggstatsplot package itself.
library(ggstatsplot) # see the selected data (we have data from 1813 movies) dplyr::glimpse(x = ggstatsplot::movies_wide)
Now that we have a clean dataset, we can start asking some interesting questions. For example, let's see if the average IMDB rating for a movie has any relationship to its budget. Additionally, let's also see which movies had a high budget but low IMDB rating by labeling those data points.
To reduce the processing time, let's only work with 30% of the dataset.
# for reproducibility set.seed(123) # to speed up the calculation, let's use only 10% of the data movies_10 <- dplyr::sample_frac(tbl = ggstatsplot::movies_long, size = 0.1) # plot ggstatsplot::ggscatterstats( data = movies_10, # dataframe from which variables are taken x = budget, # predictor/independent variable y = rating, # dependent variable xlab = "Budget (in millions of US dollars)", # label for the x-axis ylab = "Rating on IMDB", # label for the y-axis label.var = "title", # variable to use for labeling data points label.expression = "rating < 5 & budget > 100", # expression for deciding which points to label point.alpha = 0.7, point.size = 4, point.color = "grey50", marginal = TRUE, # show marginal distribution marginal.type = "density", # type of plot for marginal distribution centrality.para = "mean", # centrality parameter to be plotted margins = "both", # marginal distribution on both axes xfill = "#CC79A7", # fill for marginals on the x-axis yfill = "#009E73", # fill for marginals on the y-axis xalpha = 0.5, # transparency for the x-axis marginals yalpha = 0.75, # transparency for the y-axis marginals xsize = 1, # size for the x-axis marginals ysize = 1, # size for the y-axis marginals type = "pearson", # type of linear association title = "Relationship between movie budget and IMDB rating", caption = "Source: www.imdb.com", messages = FALSE )
There is indeed a small, but significant, positive correlation between the amount of money studio invests in a movie and the ratings given by the audiences.
type (of test) argument also accepts the following abbreviations:
"np" (for nonparametric/spearman),
In contrast to all other functions in this package, the
ggscatterstats function returns object that is not further modifiable
ggplot2. This can be avoided by not plotting the marginal distributions
marginal = FALSE). Currently trying to find a workaround this problem.
ggscatterstats() in R Notebooks or Rmarkdown
If you try including a
ggscatterstats() plot inside an R Notebook or
Rmarkdown code chunk, you'll notice that the plot doesn't get output. In
order to get a
ggscatterstats() to show up in an these contexts, you need
to save the ggscatterstats plot as a variable in one code chunk, and
explicitly print it using the
grid package in another chunk, like
# include the following code in your code chunk inside R Notebook or Markdown grid::grid.newpage() grid::grid.draw( ggstatsplot::ggscatterstats( data = ggstatsplot::movies_wide, x = budget, y = rating, marginal = TRUE, messages = FALSE ) )
Grouped analysis with
What if we want to do the same analysis do the same analysis for movies with
different MPAA (Motion Picture Association of America) film ratings (NC-17, PG,
PG-13, R)? In that case, we will have to either write a
for loop or use
purrr, none of which seem like an exciting prospect.
ggstatsplot provides a special helper function for such instances:
grouped_ggstatsplot. This is merely a wrapper function around
ggstatsplot::combine_plots. It applies
ggstatsplot across all levels of
a specified grouping variable and then combines list of individual plots
into a single plot. Note that the grouping variable can be anything: conditions
in a given study, groups in a study sample, different studies, etc.
Let's see how we can use this function to apply
ggscatterstats for all MPAA
ratings. We will be running parametric tests (Pearson's r, i.e.).
(If you set
type = "np" or
type = "r", results from non-parametric or robust
test will be displayed.)
# for reproducibility set.seed(123) # to speed up the calculation, let's use only 20% of the data # also since there are only 7 movies with NC-17 ratings, leave them out movies_20 <- dplyr::filter(.data = ggstatsplot::movies_wide, mpaa != "NC-17") %>% dplyr::sample_frac(tbl = ., size = 0.2) # plot ggstatsplot::grouped_ggscatterstats( # arguments relevant for ggstatsplot::ggscatterstats data = movies_10, title.prefix = "MPAA Rating", x = budget, y = rating, xfill = NULL, package = "ggsci", palette = "nrc_npg", grouping.var = mpaa, label.var = "title", label.expression = "rating < 5 & budget > 75", marginal.type = "boxplot", ggtheme = ggthemes::theme_tufte(), ggstatsplot.layer = FALSE, messages = FALSE, k = 2, # arguments relevant for ggstatsplot::combine_plots title.text = "Relationship between movie budget and IMDB rating", caption.text = "Source: www.imdb.com", nrow = 3, ncol = 1, labels = c("(a)","(b)","(c)","(d)") )
As seen from the plot, this analysis has revealed something interesting: The relationship we found between budget and IMDB rating holds only for PG-13 and R-rated movies.
Grouped analysis with
Although this is a quick and dirty way to explore large amount of data with
minimal effort, it does come with an important limitation: reduced flexibility.
For example, if we wanted to add, let's say, a separate type of marginal
distribution plot for each MPAA rating or if we wanted to use different types of
correlations across different levels of MPAA ratings (NC-17 has only 6 movies,
so a robust correlation would be a good idea), this is not possible. But this
can be easily done using
See the associated vignette here: https://indrajeetpatil.github.io/ggstatsplot/articles/web_only/purrr_examples.html
Different smoothing methods
Additionally, different smoothing methods can be specified. For example, if a
robust correlation (percentage bend correlation coefficient) is used, we can use
a robust smoothing function (
MASS::rlm). Additionally, we can also specify
different formulas to use for smoothing function. It is important that you
results.subtitle = FALSE since the results will no longer be relevant for
the smoothing function used. Below, four different examples are given for how to
use different smoothing functions.
library(mgcv) # for reproducibility set.seed(123) # creating a list of plots with different smoothing functions plot_list2 <- purrr::pmap( .l = list( # let's use only 5% of the data to speed up the calculations data = list(dplyr::sample_frac(tbl = ggstatsplot::movies_wide, size = 0.05)), x = "budget", y = "rating", title = list( "Robust linear model using an M estimator (rlm)", "Generalized additive model (GAM) with a penalized smoother", "Local Polynomial Regression Fitting", "Quadratic fit" ), method = list(MASS::rlm, "gam", "loess", "lm"), formula = list(y ~ x, y ~ s(x, k = 3), y ~ x, y ~ x + I(x ^ 2)), line.color = list("#009E73", "#F0E442", "#0072B2", "#D55E00"), marginal = FALSE, results.subtitle = FALSE, messages = FALSE ), .f = ggstatsplot::ggscatterstats ) # combining all individual plots from the list into a single plot using combine_plots function ggstatsplot::combine_plots( plotlist = plot_list2, title.text = "Trying out different smoothing functions with ggscatterstats", caption.text = "Source: www.imdb.com", nrow = 2, ncol = 2, labels = c("(a)", "(b)", "(c)", "(d)") )
If you find any bugs or have any suggestions/remarks, please file an issue on GitHub: https://github.com/IndrajeetPatil/ggstatsplot/issues