# Histograms_and_density_plots_for_subgroups_defined_by_factor_levels
# following to obtain my sample data:
# http://www.robin-beaumont.co.uk/virtualclassroom/book2data/pain_medication.dat
mydataframe <- read.delim("http://www.robin-beaumont.co.uk/virtualclassroom/book2data/pain_medication.dat",header=TRUE)
names(mydataframe)
str(mydataframe)

##### get it locally - ignore:
# mydataframe <- read.delim("D:\\web_sites_mine\\HIcourseweb new\\book2data\\pain_medication.dat", 
# header=TRUE)
##### 
names(mydataframe)
str(mydataframe)
# r generated  # densityPlot is in the car package
densityPlot(age~gender, data=mydataframe, bw="SJ", adjust=1, 
  kernel="gaussian")

maledata <- mydataframe[mydataframe$gender == "Male",]

femaledata <- mydataframe[mydataframe$gender == "Female",]


plot(density(maledata$age),ylim =c(0, 0.07), main ="densityplots for males/females[dotted] for age",xlab= "age (years)" )

lines(density(femaledata$age), lty = 2)

#alternative

plot(density(mydataframe$age[mydataframe$gender == "Female"]), ylim = c(0, 0.07), 
main = "densityplots for males/females[dotted] for age", xlab= "age (years)" )
# You now need to overlay the female density line.
lines(density(mydataframe$age[mydataframe$gender == "Male"]), lty = 2)

### all 4 lines on a single plot
plot (density(maledata$age[maledata$treatment == "Existing drug"], data=maledata),  
col="red", lty = 1, ylim=c(0,0.05),xlim=c(0,100),
main="Results for each treatment group according to sex & age")  
lines (density(maledata$age[maledata$treatment == "New drug"], 
data=maledata), col="green", lty = 2) 
# now for the female data
lines (density(femaledata$age[femaledata$treatment == "Existing drug"], 
data= femaledata), lty = 1, col="blue")  # females existing drug
lines (density(femaledata$age[femaledata$treatment == "New drug"], 
data= femaledata), col="black", lty = 2) # females new drug

# add a legend
legend(65, 0.05,  
c("male existing", "male new", "female existing", "female new"),
lty= c(1, 2, 1, 2), 
lwd= c(1,1,1,1), col=c("red","green","blue","black"))