# 1
  ii<-read.csv('nhanes.csv')
  plot(x=ii$lbdldl,y=ii$bpxsy1,
       xlab='LDL cholesterol (mg/dL)',
       ylab='Systolic blood pressure (mg)')

# 2 
library(ggplot2)
gg<-ggplot(data=ii,mapping=aes(x=lbdldl,y=bpxsy1))
gg+
  geom_point()+
  geom_smooth(method='loess')+
  xlab('LDL cholesterol (mg/dL)')+
  ylab('Systolic blood pressure (mg)')

# 3 
gg+
  geom_point()+
  geom_smooth(method='lm')+
  xlab('LDL cholesterol (mg/dL)')+
  ylab('Systolic blood pressure (mg)')

# 4
cor(x=ii$lbdldl,y=ii$bpxsy1,use='complete.obs')

# 5
gg<-ggplot(data=ii,mapping=aes(x=hs,y=bpxsy1))
gg+
  geom_boxplot()+
  xlab('')+
  ylab('Systolic blood pressure (mg)')

# 6
t.test(ii$bpxsy1~ii$hs)

# 7 (note that I modified the slides)
ii$hs<-relevel(ii$hs,'No') # only necessary for consistency with slides
paste(round(t.test(ii$bpxsy1~ii$hs)$conf.int,1),collapse=' to ')

# 8
gg<-ggplot(data=ii,mapping=aes(x=ridageyr,y=lbdldl,color=gender))
gg+
  geom_point()+
  xlab('Age (years)')+
  ylab('LDL cholesterol (mg/dL)')

# 9
mm<-lm(lbdldl~ridageyr+gender,data=ii)
mm

# 10
nn<-data.frame(
  ridageyr=c(52,35,47,61),
  gender=c('Male','Female','Female','Male')
)
predict(mm,nn)