Other geoms

Arguments to geom_smooth()

method uses a different model to fit the data:

ggplot(data = mpg) +
  geom_point(mapping = aes(x = displ, y = hwy)) +
  geom_smooth(mapping = aes(x = displ, y = hwy), method = "lm")

se = FALSE turns off the confidence band:

ggplot(data = mpg) +
  geom_point(mapping = aes(x = displ, y = hwy)) +
  geom_smooth(mapping = aes(x = displ, y = hwy), se = FALSE)

## `geom_smooth()` using method = 'loess' and formula 'y ~ x'

The rug

Plots marginal distributions of the data close to the axes.

ggplot(data = mpg) +
  geom_point(mapping = aes(x = displ, y = hwy)) +
  geom_rug(mapping = aes(x = displ, y = hwy))

To reduce overplotting, the “alpha” aesthetic can be set independently for each geom to a constant value:

ggplot(data = mpg) +
  geom_point(
    mapping = aes(x = displ, y = hwy),
    alpha = 0.3
  ) +
  geom_rug(
    mapping = aes(x = displ, y = hwy)
  )

ggplot(data = mpg) +
  geom_point(
    mapping = aes(x = displ, y = hwy)
  ) +
  geom_rug(
    mapping = aes(x = displ, y = hwy),
    alpha = 0.3
  )

Order of geom_...() calls

The geoms are painted in order of appearance:

ggplot(data = mpg) +
  geom_point(mapping = aes(x = displ, y = hwy)) +
  geom_smooth(mapping = aes(x = displ, y = hwy))

## `geom_smooth()` using method = 'loess' and formula 'y ~ x'

ggplot(data = mpg) +
  geom_smooth(mapping = aes(x = displ, y = hwy)) +
  geom_point(mapping = aes(x = displ, y = hwy))

## `geom_smooth()` using method = 'loess' and formula 'y ~ x'

Compare highway and city

We could add two layers, each with a different color. But this still doesn’t give us a legend.

ggplot(data = mpg) +
  geom_point(mapping = aes(x = displ, y = hwy), color = "red") +
  geom_point(mapping = aes(x = displ, y = cty), color = "blue")

We need better data transformation tools to reformat the data for plotting it in a more natural way.

Cars by drivetrain

I tried geom_histogram() and geom_col(), neither worked. The histogram is for continuous data only, for geom_col() I’d need to supply actual counts which I don’t have. The geom_bar() function computes the counts for me by applying the "count" statistical transformation to my data before plotting.

We need only the “x” aesthetic, “y” is computed automatically. drv is the relevant variable.

ggplot(mpg) +
  geom_bar(aes(x = drv))

Explicit count

The output is the same:

ggplot(data = mpg) +
  geom_bar(mapping = aes(x = drv, y = ..count..))

By default, geom_bar() plots the computed “count” aesthetic, which is by convention written with two surrounding dots.

Proportions

Plotting overall proportions changes the y scale:

ggplot(data = mpg) +
  geom_bar(mapping = aes(x = drv, y = ..prop.., group = 1))

Omitting group will plot proportions per drivetrain in each column, which are 1 by default:

ggplot(data = mpg) +
  geom_bar(mapping = aes(x = drv, y = ..prop..))

Fuel economy

We use a histogram of hwy, again only the “x” aesthetic needs to be supplied:

ggplot(data = mpg) +
  geom_histogram(mapping = aes(x = hwy))

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

The bin width should be set explicitly to avoid the warning:

ggplot(data = mpg) +
  geom_histogram(
    mapping = aes(x = hwy),
    binwidth = 1
  )

The frequency polygon is very similar. We tweak aesthetics manually in order to be able to distinguish between both layers.

ggplot(data = mpg) +
  geom_histogram(
    mapping = aes(x = hwy),
    fill = NA,
    color = "blue",
    binwidth = 1
  ) +
  geom_freqpoly(
    mapping = aes(x = hwy),
    binwidth = 1,
    size = 2
  )

Fuel economy by drivetrain

We can set the “fill” aesthetic:

ggplot(data = mpg) +
  geom_histogram(
    mapping = aes(x = hwy, fill = drv),
    binwidth = 1
  )

However, the bars are stacked, and difficult to compare to each other:

ggplot(data = mpg) +
  geom_histogram(
    mapping = aes(x = hwy, color = drv),
    fill = NA,
    binwidth = 1
  )

The frequency polygon offers a much clearer display of the same data:

ggplot(data = mpg) +
  geom_freqpoly(
    mapping = aes(x = hwy, color = drv),
    binwidth = 1
  )

Fuel economy per drivetrain (a history of failed attempts)

Can I just copy and adapt the code from the last solution?

ggplot(mpg, aes(hwy, color = drv)) +
  geom_histogram(fill = NA, color = "black", size = 0.2, binwidth = 2) +
  geom_freqpoly(color = "red", binwidth = 2)

Nope. Something’s wrong here. Maybe if I follow the template?

ggplot(mpg) +
  geom_histogram(
    aes(hwy, color = drv),
    binwidth = 2,
    fill = NA,
    color = "black",
    size = 0.2
  )

I can’t use color both as variable and manual aesthetic, ggplot2 silently uses the manual assignment! Need to be careful with assigning aesthetics.

ggplot(mpg) +
  geom_histogram(
    aes(hwy, color = drv, group = drv),
    binwidth = 2,
    size = 0.2,
    fill = NA
  ) +
  geom_freqpoly(
    aes(hwy, color = drv, group = drv),
    binwidth = 2
  )

ggplot(mpg) +
  geom_histogram(
    aes(hwy, color = drv),
    binwidth = 2,
    size = 0.2,
    fill = NA
  )

ggplot(mpg) +
  geom_freqpoly(
    aes(hwy, color = drv),
    binwidth = 2
  )