Scatter Diagrams with a Qualitative Variable

Load the HomeRun_2014 data into R.

HomeRun <- read.csv("https://sullystats.github.io/Statistics6e/Data/HomeRun_2014.csv")
head(HomeRun,n=4)

##        Date           Hitter HitterTeam           Pitcher PitcherTeam INN
## 1 9/28/2014   Rizzo, Anthony        CHC       Fiers, Mike         MIL   1
## 2 9/28/2014 Bernadina, Roger        LAD      Scahill, Rob         COL   6
## 3 9/28/2014     Duvall, Adam         SF     Stauffer, Tim          SD   4
## 4 9/28/2014      Duda, Lucas        NYM Foltynewicz, Mike         HOU   8
##          Ballpark TrueDist SpeedOffBat Elev.Angle Horiz.Angle Apex Type
## 1     Miller Park      441       109.1       22.7        86.7   81   PL
## 2 Dodger Stadi...      424       113.2       27.7        62.3   98   ND
## 3       AT&T Park      423       103.6       31.9       112.9   98   ND
## 4      Citi Field      417       106.3       26.5        73.0   83   PL

Scatter Diagrams with a Qualitative Variable

Use Mosaic. We use the following syntax when adding a qualitative variable to the command.

xyplot(y-variable ~ x-variable | qualitative variable, data = df_name)

library(mosaic)
xyplot(TrueDist ~ SpeedOffBat|Type,data=HomeRun)

Notice that there is a positive association for the JE (just enough), ND (no doubt), and PL (plenty) home run type, but ITP (inside-the-park) home runs do not appear to have a relation.

Correlations of Subsets of a Data Frame

Use the subset( ) command to create a new data frame that is a subset of an existing data frame. This will allow you to find correlation coefficients by some qualitative variable.

HomeRun_JE <- subset(HomeRun,Type=="JE")  # Data frame for JE home runs
HomeRun_ND <- subset(HomeRun,Type=="ND")  # Data frame for ND home runs
HomeRun_PL <- subset(HomeRun,Type=="PL")  # Data frame for PL home runs
HomeRun_ITP <- subset(HomeRun,Type=="ITP")  # Data frame for ITP home runs
                      
cor(TrueDist ~ SpeedOffBat, data=HomeRun_JE)

## [1] 0.5283018

cor(TrueDist ~ SpeedOffBat, data=HomeRun_ND)

## [1] 0.6691496

cor(TrueDist ~ SpeedOffBat, data=HomeRun_PL)

## [1] 0.663038

cor(TrueDist ~ SpeedOffBat, data=HomeRun_ITP)

## [1] 0.4295198