Plot panels/facets/size (solutions)

Primary exercises

Facets (grid): variable for rows and/or variable for columns.
Try each of the following facet_grid lines and understand the effects:

p <- ggplot( pulse ) +
  aes( x = weight, y = height, color = exercise, shape = gender ) +
  geom_point( size = 3, alpha = 0.8 )
p + facet_grid( . ~ exercise )

p + facet_grid( exercise ~ . )

p + facet_grid( gender ~ exercise )

p + facet_grid( exercise ~ gender )

p + facet_grid( exercise ~ gender, scales = "free" )

# p + facet_grid( . ~ exercise )
#     Here . (dot) is used to state that no facetting should be done for rows.

# p + facet_grid( exercise ~ . )
#     Here . (dot) is used to state that no facetting should be done for columns.

# p + facet_grid( exercise ~ gender, scales = "free" )
#     The scales="free" argument allows ranges on the axes to be different
#     in each row/column.

Facets (wrap): multi-level variable in multiple rows and columns.
Now compare facet_wrap with facet_grid:

p <- ggplot( pulse ) +
  aes( x = weight, y = height, color = exercise, shape = gender ) +
  geom_point( size = 3, alpha = 0.8 )
p + facet_grid( . ~ year )

p + facet_grid( year ~ . )

p + facet_wrap( ~ year )

p + facet_wrap( ~ year, scales = "free" )

# facet_grid always enforces that a single variable goes in one direction
#     (either rows or columns)
#
# facet_wrap distributes levels of the variable to fill the whole plot
#     area "nicely"

Visualize effect of running on pulse.
Reconstruct the following image based on the pulse data.
Add component coord_fixed() to enforce that unit sizes are identical for both axes.
Use geom_abline( slope = 1 ) to get the line showing where pulse1 and pulse2 are equal.
Disable the warning message.

ggplot( pulse ) +
  aes( x = pulse1, y = pulse2 ) +
  geom_point() +
  facet_wrap( ~ ran ) +
  coord_fixed() +
  geom_abline( slope = 1, color = "red", linetype = 2 ) +
  theme_bw() +
  xlab( "pulse1 (before exercise) [1/min]" ) +
  ylab( "pulse2 (after exercise) [1/min]" )

Extra exercises

Rotate axis labels.
When using facets the numbers on the bottom axis often overlap.
Modify the chart from the previous exercise by adding (after theme_bw):
theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust=1)).
vjust and hjust are numbers in range [0,1]. Understand their effect.
Try angle=45.

ggplot( pulse ) +
  aes( x = pulse1, y = pulse2 ) +
  geom_point() +
  facet_wrap( ~ ran ) +
  coord_fixed() +
  geom_abline( slope = 1, color = "red", linetype = 2 ) +
  theme_bw() +
  theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust=1)) +
  xlab( "pulse1 (before exercise) [1/min]" ) +
  ylab( "pulse2 (after exercise) [1/min]" )

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