R - Ggplot

Initialization

ggplot(df, aes(x, y, <other aesthetics>))

will define as default for all layers

• the data
• and the aesthetics

Without any argument, ggplot initializes a skeleton ggplot object which is fleshed out as layers are added.

Adding Layers

ggplot() is typically used to construct a plot incrementally, using the + operator to add layers to the existing ggplot object. This is advantageous in that the code is explicit about which layers are added and the order in which they are added.

Plot = ggplot(data, mapping) +
layer(
  stat = "",
  geom = "",
  position = "",
  geom_parms = list(),
  stat_params = list(),
)

where:

• Ggplot - Data
• mapping see Ggplot - (aes|aesthetic) (plot parameter definition)
• GGplot - Layer (data + mapping + geom + stat + position)
  • GGplot - Stat - (Statistical transformation|Statistic)
  • Ggplot - Geom (geometric objects) - type of plot
  • GGplot - Position

Example: Layers are created with the layer function but usually they are created directly through the shortcut functions geom_* (geom_point is a layer with a point geom) or stat_*)

d <- ggplot(diamonds, aes(x=carat, y=price))
d + geom_point()
d + geom_point(aes(colour = carat))

ggplot(diamonds) + geom_histogram(aes(x=price))

where:

• diamonds is the data set
• aes(x=carat, y=price) map the variable carat to x and the variable y to price.
• geom_point define a new layer with the point as geom
• geom_point(aes(colour = carat)) map the variable carat to the colour aesthetic

Blog

• Exploring Minard’s 1812 plot with ggplot2 | Andrew Heiss