draw the graph to record blood pressure vol.3

The original xts package seems to have the problem to handle time based objects which belong to the timezone other than UTC. The code below to bypass the issue to normalizes TZ parameter.

1. strip index date from the original object "bp.xts" by index()
2. convert index data which contains date and time to data format by as.Date() with the parameter "tz=Sys.timezone()" or "tz=tzone(bp.xts)". Both must return "Asia/Tokyo" in my environment.
3. rejoin the numeric data and the rebuilt index by merge().

bp.day <- merge(as.xts(as.vector(bp.xts[,1]),as.Date(index(bp.xts),tz=tzone(bp.xts))),as.vector(bp.xts[,2]))
colnames(bp.day)[1] <- "high"
colnames(bp.day)[2] <- "low"
apply.weekly(bp.day,mean)
# plot(apply.weekly(bp.day,mean),type='p')
#
# adjust mix-max of ylim by min() and max()
#
plot(apply.weekly(bp.day,mean),type='p',ylim=c( min(apply.weekly(bp.day,mean)[,2])-10,max(apply.weekly(bp.day,mean)[,1])+10))
#
# draw the horizontal line at 125
#
addSeries(as.xts(rep(125,length(apply.weekly(bp.day,mean)[,1])),index(apply.weekly(bp.day,mean))),on=1,ylim=c( min(apply.weekly(bp.day,mean)[,2])-10,max(apply.weekly(bp.day,mean)[,1])+10))
addSeries(as.xts(rep(85,length(apply.weekly(bp.day,mean)[,1])),index(apply.weekly(bp.day,mean))),on=1,ylim=c( min(apply.weekly(bp.day,mean)[,2])-10,max(apply.weekly(bp.day,mean)[,1])+10))
addSeries(as.xts(rep(mean(bp.xts[,2]),length(apply.weekly(bp.day,mean)[,1])),index(apply.weekly(bp.day,mean))),on=1,ylim=c( min(apply.weekly(bp.day,mean)[,2])-10,max(apply.weekly(bp.day,mean)[,1])+10),col=2)

addSeries(as.xts(rep(mean(bp.xts[,1]),length(apply.weekly(bp.day,mean)[,1])),index(apply.weekly(bp.day,mean))),on=1,ylim=c( min(apply.weekly(bp.day,mean)[,2])-10,max(apply.weekly(bp.day,mean)[,1])+10),col=2)

#
# below will use system's timezone instead of retrieving from the object.
#
bp.day <- merge(as.xts(as.vector(bp.xts[,1]),as.Date(index(bp.xts),tz=Sys.timezone())),as.vector(bp.xts[,2]))
colnames(bp.day)[1] <- "high"
colnames(bp.day)[2] <- "low"
apply.weekly(bp.day,mean)