clear	
clear matrix
set matsize 800
set mem 500m
cd /// your data directory here
use lahman_batting_2023.dta // assumes file converted to .dta



* drop pitchers

merge m:1 playerID using  "bb_ref_lahman_pitcher_names_match.dta", update replace // assumes file converte to .dta



keep if _merge==1 | playerID=="ruthba01" // drop all pitchers except Ruth


// drop seasons prior to 1900 and after 1999



drop if yearID<1900



//drop non AL/NL

drop if lgID != "AL" & lgID != "NL"

// rename doubles and triples

rename B b2
rename L b3

// rename other variables to conform to previous version of database

rename (G AB R H HR RBI SB CS BB SO IBB HBP SH SF) (g ab r h hr rbi sb cs bb so ibb hbp sh sf)
rename yearID yearid
rename playerID playerid
rename lgID lgid

// aggregate players season performances variables over multiple stints

collapse (sum) g ab r h b2 b3 hr rbi sb cs bb so ibb hbp sh sf, by(playerid yearid lgid)

drop if ab==0

// Calculate the batting average BA for each player-year combination
gen BA = h/ab

/// calculate weighted mean and SD for each season's BA  irrespective of league 

generate weighted_BA_product = BA * ab
egen total_weighted_BA = sum(weighted_BA_product), by(yearid)
egen total_ab = sum(ab), by(yearid)
generate weighted_mean_BA = total_weighted_BA / total_ab

generate squared_diff = (BA - weighted_mean_BA)^2
egen total_squared_diff = sum(squared_diff * ab), by(yearid)
generate weighted_variance_BA = (total_squared_diff / (total_ab - 1))
generate weighted_sd_BA = sqrt(weighted_variance_BA)




// Calculate the PA (Plate Appearances) as the sum of the relevant totals
gen PA = ab+bb+sh+sf



// adjusted Gwynn 96: Gwynn was batting title eligible under rule that adds hitless ABs

replace ab=495 if (yearid==1996 & playerid=="gwynnto01")





// Determine batting title eligibility: include title winners recogized on ad hoc criteria....
gen ba_elig = 0
replace ba_elig = 1 if (yearid < 1949 & g > 99) | ///
                    (yearid >= 1950 & yearid <= 1956 & ab > 399) | ///
                    (yearid >= 1957 & yearid <= 1960 & PA > 477) | ///
                    (yearid > 1960 & PA > 502) | ///
                    (playerid == "hargrbu01" & yearid == 1926) | ///
                    (playerid == "lombaer01" & yearid == 1942) | ///
                    (playerid == "madlobi01" & yearid == 1981) | ///
					(yearid==1996 & playerid=="gwynnto01") | ///
					(yearid==1994 & PA >345)

replace ba_elig = 1 if (yearid == 1918 & PA > 419 | yearid ==1919 & PA > 419)
replace ba_elig	= 1 if (yearid == 1972 & PA > 483)	
replace ba_elig = 1 if (yearid == 1981 & PA > 320 )
	replace ba_elig = 1 if (yearid == 1981 & PA > 356 )
	replace ba_elig = 1 if (yearid== 2020 & PA > 185)
	
	



				   
// Calculate z-score for eligible players
gen ba_zscore = .
replace ba_zscore = (BA - weighted_mean_BA) / weighted_sd_BA if ba_elig == 1

//delete batters not eligible for batting title

drop if ba_elig == 0


//recenter ba_zscore: I think this makes sense since z-scores derived from weighted mean drift from zero


* Step 1: Calculate the mean of ba_zscore
summarize ba_zscore
local mean_ba_zscore = r(mean)

* Step 2: Center ba_zscore at 0
replace ba_zscore = ba_zscore - `mean_ba_zscore'


//normalize to 0 to 100 scale: an alternative way to normalize data w/ zero as lowest & 100 as highest
//should be used in any event to enable generation of BA+ scale

su ba_zscore
gen normal_z_ba=((ba_zscore-r(min))/(r(max)-r(min)))*100



/// normalize to BA+ scale
su normal_z_ba

gen ba_plus = 100*(normal_z_ba/r(mean))


/// shrink data set to title winners



* Step 1: Sort the data by yearid, lgid, and BA in descending order
gsort yearid lgid -BA

* Step 2: Generate a ranking variable
by yearid lgid: gen rank = _n

** substitute snuffy stirnweis for lazorjo01: the criteria for ba title eligibility seemed malleable... 
//Johnny Lazor should have won given then-previaling 100 game played criterion

replace rank = 1 if playerid=="stirnsn01" & year==1945
drop if playerid=="lazorjo01"

* Step 3: Filter the data to keep only the top BA value for each yearid and lgid
keep if rank == 1



* add lahman names
rename playerid playerID


merge m:m playerID using "lahman_names.dta"

keep if ba_elig==1


/// generate probability density plot for title-winners 

 kdensity ba_plus, yscale(off) recast(area) xtitle("") xlabel(120(10)200, nogrid) scale(1)   ///
					title ("")  graphregion( color(white) ) lcolor(black) fcolor(white)  ylabel(, nogrid noticks nolabels) xlabel(, nogrid ) ///
					lwidth(medium) xscale(range(120 200)) lpattern(solid)  ///
									 legend(off) note("") 
//export results to excel file

export excel using [desired file name here], firstrow(variables) replace