Layers

What is a Layer?

A layer added ggplot() can be a geom…

• The type of geometric object
• The statistic mapped to that object
• The data set from which to obtain the statistic

… or a position adjustment to the scales

• Changing the axes scale
• Changing the color gradient

Layer Examples

More geoms described at http://docs.ggplot2.org/current/

Piecing Things Together

Want to build a map using NOAA data

• Coordinate system (mapping Long-Lat to X-Y)
• Add layer of state outlines
• Add layer of points for float locations
• Add layers for Oil Rig marker and label
• Adjust the range of x and y scales

The Result

ggplot() +
    geom_path(data = states, aes(x = long, y = lat, group = group)) + 
    geom_point(data = floats, aes(x = Longitude, y = Latitude, colour = callSign)) +   
    geom_point(aes(x, y), shape = "x", size = 5, data = rig) + 
    geom_text(aes(x, y), label = "BP Oil Rig", size = 5, data = rig, hjust = -0.1) + 
    xlim(c(-91, -80)) + 
    ylim(c(22, 32)) + coord_map()

ggplot is pipeable!

We can pass data as the first argument to ggplot()… meaning we can pipe to it!

Tidyverse FTW

library(tidyverse)
data(baseball, package="plyr")

baseball %>%
  filter(ab > 0) %>% #only players that have ever had an at bat
  group_by(year) %>%
  mutate(ba = h/ab,
         mean_ba = mean(h/ab)) %>%
  ggplot() +
  geom_point(aes(year, ba), alpha = .1) +
  geom_line(aes(year, mean_ba), colour = "blue")

French fries

During a ten week sensory experiment, 12 individuals were asked to assess taste of french fries on several scales (how potato-y, buttery, grassy, rancid, paint-y do the fries taste?)

French fries were fried in one of three different oils, and each week individuals had to assess six batches of french fries (all three oils, replicated twice)