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Finds estimates of true batting averages for all batters against a specific pitcher.
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# loading in Retrosheet data for the seasons 1960 through 2013 from my website | |
load(url("http://bayes.bgsu.edu/baseball/pbp.1960.1979.Rdata")) | |
load(url("http://bayes.bgsu.edu/baseball/pbp.1980.1999.Rdata")) | |
load(url("http://bayes.bgsu.edu/baseball/pbp.2000.2013.Rdata")) | |
batter.matchup.ggplot <- function(Name, graph=TRUE, retroid=FALSE){ | |
# this function assumes the data frames pbp.60.79, pbp.80.99, and pbp.00.13 are | |
# in the workspace | |
fit.model <- function(y, n){ | |
require(LearnBayes) | |
fit <- laplace(betabinexch, c(1, 1), cbind(y, n))$mode | |
eta <- exp(fit[1]) / (1 + exp(fit[1])) | |
K <- exp(fit[2]) | |
Estimate <- (y + K * eta) / (n + K) | |
list(K=K, eta=eta, Estimate=Estimate) | |
} | |
require(dplyr) | |
require(Lahman) | |
if(retroid==FALSE){ | |
name <- unlist(strsplit(Name, split=" ")) | |
retro.id <- filter(Master, nameLast==name[2], | |
nameFirst==name[1])$retroID[1]} else | |
retro.id <- Name | |
d1 <- filter(pbp.60.79, PIT_ID==retro.id, BAT_EVENT_FL==TRUE) | |
d2 <- filter(pbp.80.99, PIT_ID==retro.id, BAT_EVENT_FL==TRUE) | |
d3 <- filter(pbp.00.13, PIT_ID==retro.id, BAT_EVENT_FL==TRUE) | |
d <- rbind(d1, d2, d3) | |
S <- summarize(group_by(d, BAT_ID), | |
AB=sum(AB_FL), H=sum(H_FL >= 1)) | |
S <- filter(S, AB > 0) | |
get.name <- function(j){ | |
F <- filter(Master, retroID==S$BAT_ID[j]) | |
paste(F$nameFirst, F$nameLast)} | |
S$Batter.Name <- sapply(1:dim(S)[1], get.name) | |
M <- fit.model(S$H, S$AB) | |
if(graph==TRUE){ | |
print(c(eta=M$eta, K=M$K)) | |
S$Estimate <- M$Estimate | |
S <- S[order(S$Estimate, decreasing=TRUE), ] | |
S$Num <- 1:dim(S)[1] | |
require(ggplot2) | |
pt <- ggplot(S, aes(AB, Estimate)) + geom_point(size=3) + | |
geom_hline(aes(yintercept=sum(H) / sum(AB)), | |
color="red", size=2) + | |
ggtitle(paste(Name, "Smoothed Averages")) + | |
theme(plot.title = element_text(size = rel(3), | |
color = "blue")) + | |
theme(axis.title = element_text(size = rel(2))) + | |
geom_text(data=subset(S, Num < 3 | Num > dim(S)[1] - 2), | |
aes(AB, Estimate, label=Batter.Name), | |
color="red") | |
print(pt) | |
print(head(S)) | |
print(tail(S)) | |
S} else c(M$K, M$eta) | |
} |
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