R script and function to plot the career trajectory for a MLB baseball hitter

trajectory.2014.R

#######################################################
# trajectory.2014.R
# script and function to plot a career trajectory for a batter
# in major league baseball
# requires installation of packages
# Lahman, dplyr, and ggplot2
#
# once this script is sourced, then graph trajectory of
# Alex Rodriquez's home run rates by typing
# plot.trajectory("Alex Rodriguez", "HR")
#######################################################

# setup work
library(Lahman)
library(dplyr) 

# create new data frame Batting.new by
# collapsing over stint variable - took 0.34 seconds

Batting.new <- summarise(group_by(Batting, playerID, yearID), 
                        AB = sum(AB),
                        H = sum(H),
                        X2B = sum(X2B),
                        X3B = sum(X3B),
                        HR = sum(HR),
                        SB = sum(SB),
                        BB = sum(BB),
                        SO = sum(SO),
                        HBP = sum(HBP),
                        SF = sum(SF),
                        SH = sum(SH))

myrecode <- function(data, var){
  data[, var] <- ifelse(is.na(data[, var]), 0, data[, var])
  data
}
Batting.new <- myrecode(Batting.new, "SF")
Batting.new <- myrecode(Batting.new, "SH")

# define plate appearance variable
Batting.new$PA <- with(Batting.new, AB + BB + HBP + SF + SH)

# add age variable
Master$birthyear <- with(Master, 
                  ifelse(birthMonth >= 7, birthYear + 1, birthYear))
Batting.new <- merge(Batting.new, 
                 Master[, c("playerID", "nameFirst", "nameLast", "birthyear")],
                 by="playerID")
Batting.new$Age <- with(Batting.new, yearID - birthyear)

# add first and last years
library(dplyr)
C.Years <- summarise(group_by(Batting, playerID), 
                         fYear=min(yearID),
                         lYear=max(yearID))
Batting.new <- merge(Batting.new, C.Years, by="playerID")

# function to plot trajectory
plot.trajectory <- function(name, stat="H", denom="AB", num=1){
  require(ggplot2)
  firstlast <- unlist(strsplit(name," "))
  playerids <- unique(subset(Batting.new, 
                     nameFirst==firstlast[1] & 
                     nameLast==firstlast[2])$playerID)
  d <- subset(Batting.new, playerID==playerids[num])
  d$Rate <- d[, stat] / d[, denom]
  print(ggplot(d, aes(Age, Rate)) + 
        geom_point(size=5, color="red") +
        geom_smooth(method="loess", size=3) +
        theme(axis.text = element_text(size = rel(2))) + 
        theme(axis.title = element_text(size = rel(2))) +
        theme(plot.title = element_text(size = rel(2))) +
    labs(title = 
           paste(stat,"/",denom,
                 "Career Trajectory of", name,
                  d$fYear, "to",
                  d$lYear)))
}