Annotating select points on an X-Y plot using ggplot2

  qplot(UZR.150, wRAA, data = outfield)



So that must be Raul Ibanez over there on the far left. It’s clear from this plot that his hitting (represented on the Y axis) is just above the 0 line, and a long way below the outfielders who are hitting up a storm. It’s worth keeping in mind that Ibanez’s hitting contribution is helped to some degree by the fact that just over one-third of his plate appearances so far this year (126 of 187) have been as a designated hitter or pinch hitter.

In looking at this plot, you might ask the same thing I did: Where are the rest of the Mariners outfielders, and who are the stars of the X and Y axes?

Code to set up the tables for plotting

The next chunk of code takes three approaches to identifying groups and individuals on the chart. We don’t want to plot the names of all 110 players, that would be utterly illegible. Instead, we’ll focus on three groups: the Seattle Mariners, the top UZR.150 players, and the top wRAA players. The Mariners player points and names will be navy blue, and others in black. The code will label the Mariners players and the top performers on the wRAA axis automatically, and a manual approach will be adopted to create the code necessary to identify the top UZR players.

But before plotting the results, new variables in the “outfield” table are created that have the names of the Mariners players, the UZR stars, and the wRAA stars.

# create new MarinerNames field that contains only the name of Mariners
# players (plagarized from Winston Chang’s R Graphics Cookbook Recipe 5.11)
outfield$MarinerNames = outfield$Name
idx = (outfield$Team.x == “Mariners”)
outfield$MarinerNames[!idx] = NA
# create a new table, taking a subset that has only the Mariners players
Mariners = subset(outfield, Team.x == “Mariners”)
# add the names of the UZR stars to outfield$Table2 sort the table by
# wRAA, then add the names of the top 4 wRAA stars
outfield$wRAAstars = outfield$Name
outfield = outfield[order(-outfield$wRAA), ]
outfield$wRAAstars[5:110] = NA
# sort the table by UZR.150, then copy the first 3 names
outfield$UZRstars = outfield$Name
outfield = outfield[order(-outfield$UZR.150), ]
outfield$UZRstars[4:110] = NA
#

The final plot code

# the full ggplot verion, creating an object called “WARcht”
WARcht = ggplot(outfield, aes(x=UZR.150, y=wRAA)) + #
   geom_point(colour=”gray60″, size=2.0) + # set the colour and size of the points
   theme_bw() + # and use the “background white” theme
   ggtitle(“Everyday Outfielders, 2013 [to 2013-06-15]”) # and put a title on the plot
#
# start with WARcht, add geom_text() [for auto labels] and annotate() [for manual labels and arrows]
#
#
WARcht + # print the chart object
   geom_text(aes(label=MarinerNames), size=4, face=”bold”, colour=”navyblue”,
      vjust=0, hjust=-0.1) + # add the names of the Mariners players
   geom_text(aes(label=wRAAstars), size=3, face=”bold”,
      vjust=0, hjust=-0.1) + # add the names of the top wRAA players
   annotate(“text”, label=”Shane Victorino”, x=40, y=3, size=3, 
      face=”bold.italic”) + # manually place the label for Shane Victorino
   annotate(“segment”, x=50, y=2, xend=51.7, yend=-0.4, size=0.5,
      arrow=arrow(length=unit(.2, “cm”))) + # manually place the Victorino arrow
   annotate(“text”, label=”Craig Gentry”, x=40, y=-7.0, size=3,
      face=”bold.italic”) +
   annotate(“segment”, x=42, y=-6.6, xend=40.9, yend=-4.0, size=0.5, 
      arrow=arrow(length=unit(.2, “cm”))) +
   annotate(“text”, label=”A.J. Pollock”, x=49, y=-2.5, size=3,    
      face=”bold.italic”) +
   geom_point(data=Mariners, aes(x=UZR.150, y=wRAA), colour=”navyblue”, size=4) # over-plot the points for the Mariners players

The final analysis

In addition to Raul Ibanez, there are four other Mariners outfielders who have logged more than 200 innings. The only one on the plus side of the UZR.150 ledger is Jason Bay, at 5.5. And along with Ibanez, only Michael Morse has a positive wRAA. Put it another way, all five are more or less in the lower right-hand quadrant of the chart. So yes, it’s a fair assessment that the Mariners outfield is a disaster.

The Major League outfielders who are the top hitters (the Y axis on the chart) are led by the Rockies’ Carlos Gonzalez (at 28.1), ahead of Shin-Soo Choo (21.2) and Mike Trout (19.8). And defensively (the X axis), Shane Victorino leads with 51.9, followed by Craig Gentry (40.9) and A.J. Pollock (39.1).

The only outfielder who shines on both dimensions is the Brewers’ Carlos Gomez, who stands in fourth place on both UZR.150 and wRAA. As the chart shows, so far this season he’s in a class by himself.

Note: the code above can be found in a gist at github.

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