ggplot2 - Essentials

Introduction

ggplot2 is a powerful and a flexible R package, implemented by Hadley Wickham, for producing elegant graphics.

The concept behind ggplot2 divides plot into three different fundamental parts: Plot = data + Aesthetics + Geometry.

The principal components of every plot can be defined as follow:

  • data is a data frame
  • Aesthetics is used to indicate x and y variables. It can also be used to control the color, the size or the shape of points, the height of bars, etc…..
  • Geometry defines the type of graphics (histogram, box plot, line plot, density plot, dot plot, ….)

There are two major functions in ggplot2 package: qplot() and ggplot() functions.

  • qplot() stands for quick plot, which can be used to produce easily simple plots.
  • ggplot() function is more flexible and robust than qplot for building a plot piece by piece.

This document provides R course material for producing different types of plots using ggplot2.

If you want be highly effective, download our book: Guide to Create Beautiful Graphics in R

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Install and load ggplot2 package

# Installation
install.packages('ggplot2')
# Loading
library(ggplot2)

Data format and preparation

The data should be a data.frame (columns are variables and rows are observations).

The data set mtcars is used in the examples below:

# Load the data
data(mtcars)
df <- mtcars[, c("mpg", "cyl", "wt")]
head(df)
##                    mpg cyl    wt
## Mazda RX4         21.0   6 2.620
## Mazda RX4 Wag     21.0   6 2.875
## Datsun 710        22.8   4 2.320
## Hornet 4 Drive    21.4   6 3.215
## Hornet Sportabout 18.7   8 3.440
## Valiant           18.1   6 3.460

Plotting with ggplot2

  1. qplot(): Quick plot with ggplot2
    • Scatter plots
    • Bar plot
    • Box plot, violin plot and dot plot
    • Histogram and density plots
  2. Box plots
    • Basic box plots
    • Box plot with dots
    • Change box plot colors by groups
      • Change box plot line colors
      • Change box plot fill colors
    • Change the legend position
    • Change the order of items in the legend
    • Box plot with multiple groups
    • Functions: geom_boxplot(), stat_boxplot(), stat_summary()

  1. Violin plots
    • Basic violin plots
    • Add summary statistics on a violin plot
      • Add mean and median points
      • Add median and quartile
      • Add mean and standard deviation
    • Violin plot with dots
    • Change violin plot colors by groups
      • Change violin plot line colors
      • Change violin plot fill colors
    • Change the legend position
    • Change the order of items in the legend
    • Violin plot with multiple groups
    • Functions: geom_violin(), stat_ydensity()

  1. Dot plots
    • Basic dot plots
    • Add summary statistics on a dot plot
      • Add mean and median points
      • Dot plot with box plot and violin plot
      • Add mean and standard deviation
    • Change dot plot colors by groups
    • Change the legend position
    • Change the order of items in the legend
    • Dot plot with multiple groups
    • Functions: geom_dotplot()

  1. Stripcharts
    • Basic stripcharts
    • Add summary statistics on a stripchart
      • Add mean and median points
      • Stripchart with box blot and violin plot
      • Add mean and standard deviation
    • Change point shapes by groups
    • Change stripchart colors by groups
    • Change the legend position
    • Change the order of items in the legend
    • Stripchart with multiple groups
    • Functions: geom_jitter(), stat_summary()

  1. Density plots
    • Basic density plots
    • Change density plot line types and colors
    • Change density plot colors by groups
      • Calculate the mean of each group :
      • Change line colors
      • Change fill colors
    • Change the legend position
    • Combine histogram and density plots
    • Use facets
    • Functions: geom_density(), stat_density()

  1. Histogram plots
    • Basic histogram plots
    • Add mean line and density plot on the histogram
    • Change histogram plot line types and colors
    • Change histogram plot colors by groups
      • Calculate the mean of each group
      • Change line colors
      • Change fill colors
    • Change the legend position
    • Use facets
    • Functions: geom_histogram(), stat_bin(), position_identity(), position_stack(), position_dodge().

  1. Scatter plots
    • Basic scatter plots
    • Label points in the scatter plot
      • Add regression lines
      • Change the appearance of points and lines
    • Scatter plots with multiple groups
      • Change the point color/shape/size automatically
      • Add regression lines
      • Change the point color/shape/size manually
    • Add marginal rugs to a scatter plot
    • Scatter plots with the 2d density estimation
    • Scatter plots with ellipses
    • Scatter plots with rectangular bins
    • Scatter plot with marginal density distribution plot
    • Functions: geom_point(), geom_smooth(), stat_smooth(), geom_rug(), geom_density_2d(), stat_density_2d(), stat_bin_2d(), geom_bin2d(), stat_summary_2d(), geom_hex() (see stat_bin_hex()), stat_summary_hex()

  1. Bar plots
    • Basic bar plots
      • Bar plot with labels
      • Bar plot of counts
    • Change bar plot colors by groups
      • Change outline colors
      • Change fill colors
    • Change the legend position
    • Change the order of items in the legend
    • Bar plot with multiple groups
    • Bar plot with a numeric x-axis
    • Bar plot with error bars
    • Functions: geom_bar(), geom_errorbar()

  1. Line plots
    • Line types in R
    • Basic line plots
    • Line plot with multiple groups
      • Change globally the appearance of lines
      • Change automatically the line types by groups
      • Change manually the appearance of lines
    • Functions: geom_line(), geom_step(), geom_path(), geom_errorbar()

  1. Error bars
    • Add error bars to a bar and line plots
      • Bar plot with error bars
      • Line plot with error bars
    • Dot plot with mean point and error bars
    • Functions: geom_errorbarh(), geom_errorbar(), geom_linerange(), geom_pointrange(), geom_crossbar(), stat_summary()
  2. Pie chart
    • Simple pie charts
    • Change the pie chart fill colors
    • Create a pie chart from a factor variable
    • Functions: coord_polar()

  1. QQ plots
    • Basic qq plots
    • Change qq plot point shapes by groups
    • Change qq plot colors by groups
    • Change the legend position
    • Functions: stat_qq()

  1. ECDF plots

  1. ggsave(): Save a ggplot
    • print(): print a ggplot to a file
    • ggsave: save the last ggplot
    • Functions: print(), ggsave()

Graphical parameters

  1. Main title, axis labels and legend title
    • Change the main title and axis labels
    • Change the appearance of the main title and axis labels
    • Remove x and y axis labels
    • Functions: labs(), ggtitle(), xlab(), ylab(), update_labels()

  1. Legend position and appearance
    • Change the legend position
    • Change the legend title and text font styles
    • Change the background color of the legend box
    • Change the order of legend items
    • Remove the plot legend
    • Remove slashes in the legend of a bar plot
    • guides() : set or remove the legend for a specific aesthetic
    • Functions: guides(), guide_legend(), guide_colourbar()

  1. Change colors automatically and manually
    • Use a single color
    • Change colors by groups
      • Default colors
      • Change colors manually
      • Use RColorBrewer palettes
      • Use Wes Anderson color palettes
    • Use gray colors
    • Continuous colors: Gradient colors
    • Functions:
      • Brewer palettes: scale_colour_brewer(), scale_fill_brewer(), scale_color_brewer()
      • Gray scales: scale_color_grey(), scale_fill_grey()
      • Manual colors: scale_color_manual(), scale_fill_manual()
      • Hue colors: scale_colour_hue()
      • Gradient, continuous colors: scale_color_gradient(), scale_fill_gradient(), scale_fill_continuous(), scale_color_continuous()
      • Gradient, diverging colors: scale_color_gradient2(), scale_fill_gradient2(), scale_colour_gradientn()

  1. Point shapes, colors and size
    • Change the point shapes, colors and sizes automatically
    • Change point shapes, colors and sizes manually
    • Functions: scale_shape_manual(), scale_color_manual(), scale_size_manual()

Points shapes available in R:

r point shape

  1. Add text annotations to a graph
    • Text annotations using the function geom_text
    • Change the text color and size by groups
    • Add a text annotation at a particular coordinate
    • annotation_custom : Add a static text annotation in the top-right, top-left, …
    • Functions: geom_text(), annotate(), annotation_custom()

  1. Line types
    • Line types in R
    • Basic line plots
    • Line plot with multiple groups
      • Change globally the appearance of lines
      • Change automatically the line types by groups
      • Change manually the appearance of lines
    • Functions: scale_linetype(), scale_linetype_manual(), scale_color_manual(), scale_size_manual()

  1. Themes and background colors
    • Quick functions to change plot themes
    • Customize the appearance of the plot background
      • Change the colors of the plot panel background and the grid lines
      • Remove plot panel borders and grid lines
      • Change the plot background color (not the panel)
    • Use a custom theme
      • theme_tufte : a minimalist theme
      • theme_economist : theme based on the plots in the economist magazine
      • theme_stata: theme based on Stata graph schemes.
      • theme_wsj: theme based on plots in the Wall Street Journal
      • theme_calc : theme based on LibreOffice Calc
      • theme_hc : theme based on Highcharts JS
      • Functions: theme(), theme_bw(), theme_grey(), theme_update(), theme_blank(), theme_classic(), theme_minimal(), theme_void(), theme_dark(), element_blank(), element_line(), element_rect(), element_text(), rel()

  1. Axis scales and transformations
    • Change x and y axis limits
      • Use xlim() and ylim() functions
      • Use expand_limts() function
      • Use scale_xx() functions
    • Axis transformations
      • Log and sqrt transformations
      • Format axis tick mark labels
      • Display log tick marks
    • Format date axes
      • Plot with dates
      • Format axis tick mark labels
      • Date axis limits
    • Functions:
      • xlim(), ylim(), expand_limits() : x, y axis limits
      • scale_x_continuous(), scale_y_continuous()
      • scale_x_log10(), scale_y_log10(): log10 transformation
      • scale_x_sqrt(), scale_y_sqrt(): sqrt transformation
      • coord_trans()
      • scale_x_reverse(), scale_y_reverse()
      • annotation_logticks()
      • scale_x_date(), scale_y_date()
      • scale_x_datetime(), scale_y_datetime()

  1. Axis ticks: customize tick marks and labels, reorder and select items
    • Change the appearance of the axis tick mark labels
    • Hide x and y axis tick mark labels
    • Change axis lines
    • Set axis ticks for discrete and continuous axes
      • Customize a discrete axis
        • Change the order of items
        • Change tick mark labels
        • Choose which items to display
      • Customize a continuous axis
        • Set the position of tick marks
        • Format the text of tick mark labels
    • Functions: theme(), scale_x_discrete(), scale_y_discrete(), scale_x_continuous(), scale_y_continuous()

  1. Add straight lines to a plot: horizontal, vertical and regression lines
    • geom_hline : Add horizontal lines
    • geom_vline : Add vertical lines
    • geom_abline : Add regression lines
    • geom_segment : Add a line segment
    • Functions: geom_hline(), geom_vline(), geom_abline(), geom_segment()

  1. Rotate a plot: flip and reverse
    • Horizontal plot : coord_flip()
    • Reverse y axis
    • Functions: coord_flip(), scale_x_reverse(), scale_y_reverse()

  1. Faceting: split a plot into a matrix of panels
    • Facet with one variable
    • Facet with two variables
    • Facet scales
    • Facet labels
    • facet_wrap
    • Functions: facet_grid(), facet_wrap(), label_both(), label_bquote(), label_parsed()

Extensions to ggplot2: R packages and functions

Acknowledgment

Infos

This analysis was performed using R (ver. 3.2.4) and ggplot2 (ver 2.1.0).


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