[R] stacked area chart

[Dimitri Liakhovitski]

Dear R-ers!

Asking for your help with building the stacked area chart for the
following simple data (several variables - with date on the X axis):

### Creating a data set
my.data<-data.frame(date=c(20080301,20080402,20080503,20090301,20090402,20090503,20100301,20100402,20100503),
x=c(1.1,1.0,1.6,1,2,1.5,2.1,1.3,1.9),y=c(-4,-3,-6,-5,-7,-5.2,-6,-4,-4.9),
z=c(-0.2,-0.3,-0.4,-0.1,-0.2,-0.05,-0.2,-0.15,-0.06),a=c(4,3,5,5,6,7,5,6,4))
my.data$date<-as.character(my.data$date)
my.data$date<-as.Date(my.data$date,"%Y%m%d")
(my.data)

I'd like the variables whose column values sum up to a negative number
to be below zero on that chart and those that add up to a positive
number to be above zero in the chart. I am calculating values for ylim
and for the order of the variable entry (bottom up) like this:

positives<-which(colSums(my.data[2:ncol(my.data)])>0) # which vars
have positive column sums?
negatives<-which(colSums(my.data[2:ncol(my.data)])<0) # which vars
have negative column sums?

y.max<-1.1*max(rowSums(my.data[names(positives)])) # the max on the y
axis of the chart
y.min<-1.1*min(rowSums(my.data[names(negatives)])) # the min on the y
axis of the chart
ylim <- c(y.min, y.max)  # ylim for the stacked area chart

order.positives<-rev(rank(positives))
order.negatives<-rev(rank(negatives))
order<-c(order.negatives,order.positives)
order.of.vars<-names(order)   # the order of variables on the chart - bottom up
### so, the bottom-most area should be for z, and the second from the
bottom area- for y (above z) - they'll be below zero
### and above zero we'll have a first and x second (on top of a).

Thanks a lot for your advice!

-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com