Facet_wrap() function

facet_wrap() divides one ggplot visualization into separate panels defined by the levels or combinations of conditioning variables. Each panel shows the same kind of chart for a different subgroup, making comparisons easier while retaining a shared visual structure. section 2.5.3 section 9.5.2

For a single conditioning variable, use facet_wrap(~variable). If Born2 has two levels, facet_wrap(~Born2) produces two panels. In the NBA draft example, each panel contains boxplots of career win shares by college attendance, separated by players’ birthplace grouping. section 2.5.3

p2 <- ggplot(draft, aes(x = College2, y = WS)) + 
 geom_boxplot(color = "orange4", fill = "orange1") +  
 labs(title = "Career Win Shares Distribution of 
      NBA First-Round Selections",
      x = "", 
      y = "Career Win Shares", 
      subtitle = "2000-09 NBA Drafts") + 
 stat_summary(fun = mean, geom = "point", shape = 20, 
              size = 8, color = "white", fill = "white") + 
 theme(plot.title = element_text(face = "bold")) +
 facet_wrap(~Born2) + 
 scale_x_discrete(breaks = c(0, 1),
                  labels = c("No College", "College"))
print(p2)

This plot layers boxplots and mean markers, then uses facet_wrap(~Born2) to create a separate comparison panel for each birthplace level. scale_x_discrete() replaces coded college values with readable labels. section 2.5.3

With two conditioning variables, facet_wrap(teamDayOff~opptDayOff) creates a panel for each combination. Twenty-five home-team and opponent days-off permutations are arranged automatically in a 5 × 5 grid. section 9.5.2

Facet layout and scales can be adjusted when a comparison needs a different presentation:

• Add ncol to set the number of columns; the number of rows changes to accommodate the fixed number of panels. section 9.5.2
• Keep fixed scales to harmonize axes across panels, or set scales to free for independently scaled panel axes. section 9.5.2
• Use xlim() to leave room for labels when bar values extend toward the edge of each panel. section 9.5.2

ggplot(data = finaldf, aes(x = n, y = teamLoc, fill = teamLoc)) +
 geom_bar(stat = "identity") +
 facet_wrap(teamDayOff~opptDayOff) +
 labs(title = 
        "Home and Away Win Totals Broken Down by Days Off Permutations", 
      subtitle = "2012-13 to 2017-18 Regular Seasons", 
      caption = "Top Numbers: Home team prior days off
      Bottom Numbers: Away team prior days off",
      x = "Win Totals",
      y = "") +
 xlim(0,1500) +
 geom_text(aes(label = n, vjust = 0.1, hjust = -0.1)) +
 theme(plot.title = element_text(face = "bold")) +
 theme(legend.position = "none")

This complete ggplot call combines geom_bar(), facet_wrap(teamDayOff~opptDayOff), xlim(), and geom_text() to display home and away win totals for every days-off permutation. section 9.5.2