How to calculate number of occurrences per minute for a large dataset

Question

I have a dataset with 500k appointments lasting between 5 and 60 minutes.

tdata <- structure(list(Start = structure(c(1325493000, 1325493600, 1325494200,         


        

Answer 1

Is this any better.

Create a blank time vector and a blank count vector.

 vecTime <- seq(from=tdata$Start[1],to=tdata$End[nrow(tdata)],by=60)
 addz <- array(0,length(vecTime))
 remz <- array(0,length(vecTime))


 startAgg <- aggregate(tdata$Start,by=list(tdata$Start),length)
 endAgg <- aggregate(tdata$End,by=list(tdata$End),length)
 addz[which(vecTime %in% startAgg$Group.1 )] <- startAgg$x
 remz[which(vecTime %in% endAgg$Group.1)] <- -endAgg$x
 res <- data.frame(time=vecTime,occupancy=cumsum(addz + remz))