Agenda

build scatter plots
modify point
- color
- fill
- alpha
- shape
- size
fit regression line

Intro

A scatter plot displays the relationship between two continuous variables. In ggplot2, we can build a scatter plot using geom_point(). Scatterplots can show you visually

the strength of the relationship between the variables
the direction of the relationship between the variables
and whether outliers exist

Libraries

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

Basic Plot

ggplot(mtcars) +
  geom_point(aes(disp, mpg))

Jitter

ggplot(mtcars) +
  geom_point(aes(disp, mpg), position = 'jitter')

Jitter

ggplot(mtcars) +
  geom_jitter(aes(disp, mpg))

Aesthetics

Now let us modify the aesthetics of the points. There are two ways:

map them to variables using the aes() function
specify values

Map Color to Variable (Categorical)

ggplot(mtcars) +
  geom_point(aes(disp, mpg, color = factor(cyl)), 
             position = 'jitter')

Map Color to Variable (Continuous)

ggplot(mtcars) +
  geom_point(aes(disp, mpg, color = hp), 
             position = 'jitter')

Specify Value for Color

ggplot(mtcars) +
  geom_point(aes(disp, mpg), color = 'blue', 
             position = 'jitter')

Specify Value for Alpha

ggplot(mtcars) +
  geom_point(aes(disp, mpg), color = 'blue', alpha = 0.4, 
             position = 'jitter')

Map Shape to Variable

ggplot(mtcars) +
  geom_point(aes(disp, mpg, shape = factor(cyl)),
             position = 'jitter')

Specify Value for Shape

ggplot(mtcars) +
  geom_point(aes(disp, mpg), shape = 3,
             position = 'jitter')

Map Size to Variable

ggplot(mtcars) +
  geom_point(aes(disp, mpg, size = hp), color = 'blue',
             position = 'jitter')

Specify Value for Size

ggplot(mtcars) +
  geom_point(aes(disp, mpg), size = 3,
             position = 'jitter')

Regression Line

ggplot(mtcars, aes(disp, mpg)) +
  geom_point(position = 'jitter') +
  geom_smooth(method = 'lm', se = FALSE)

Regression Line - Conf. Interval

ggplot(mtcars, aes(disp, mpg)) +
  geom_point(position = 'jitter') +
  geom_smooth(method = 'lm', se = TRUE)

Regression Line - Loess Method

ggplot(mtcars, aes(disp, mpg)) +
  geom_point(position = 'jitter') +
  geom_smooth(method = 'loess', se = FALSE)

Fit Line - Intercept & Slope

ggplot(mtcars, aes(disp, mpg)) +
  geom_point(position = 'jitter') +
  geom_abline(intercept = 29.59985, slope = -0.04122)