Histograms

Introduzione alla visualizzazione dei dati con ggplot2

Rick Scavetta

Founder, Scavetta Academy

Common plot types

Plot type	Possible Geoms
Scatter plots	points, jitter, abline, smooth, count
Bar plots	histogram, bar, col, errorbar
Line plots	line, path

Histograms

ggplot(iris, aes(x = Sepal.Width)) + 
  geom_histogram()

A plot of binned values
- i.e. a statistical function

`stat_bin()` using `bins = 30`.
Pick better value with `binwidth`.

Default of 30 even bins

ggplot(iris, aes(x = Sepal.Width)) + 
  geom_histogram()

A plot of binned values
- i.e. a statistical function

# Default bin width:
diff(range(iris$Sepal.Width))/30

[1] 0.08

Intuitive and meaningful bin widths

ggplot(iris, aes(x = Sepal.Width)) + 
  geom_histogram(binwidth = 0.1)

Always set a meaningful bin widths for your data.
No spaces between bars.

Re-position tick marks

ggplot(iris, aes(x = Sepal.Width)) + 
  geom_histogram(binwidth = 0.1,
                 center = 0.05)

Always set a meaningful bin widths for your data.
No spaces between bars.
X axis labels are between bars.

Different Species

ggplot(iris, aes(x = Sepal.Width, 
                 fill = Species)) + 
  geom_histogram(binwidth = .1, 
                 center = 0.05)

Default position is "stack"

ggplot(iris, aes(x = Sepal.Width,
                 fill = Species)) + 
  geom_histogram(binwidth = .1, 
                 center = 0.05,
                 position = "stack")

position = "dodge"

ggplot(iris, aes(x = Sepal.Width, 
                 fill = Species)) + 
  geom_histogram(binwidth = .1, 
                 center = 0.05, 
                 position = "dodge")

position = "fill"

ggplot(iris, aes(x = Sepal.Width, 
                 fill = Species)) + 
  geom_histogram(binwidth = .1, 
                 center = 0.05, 
                 position = "fill")

Final Slide

Introduzione alla visualizzazione dei dati con ggplot2