R/msectopoints.R

In erpR: Event-Related Potentials (ERP) Analysis, Graphics and Utility Functions

msectopoints<-function(a, lengthsegment, startmsec, endmsec){
  
  if (is.null(startmsec)|is.null(endmsec)){
    stop("startmsec and endmsec must be specified", call.=F)
  }
  
  #lengthsegment=lengthsegment-1
  totmsec=endmsec-(startmsec) #total duration in msec
  msecstep=(lengthsegment-1)/totmsec #how many points is a msec. 
  # notice the - 1. This is because it doesn't make sense to say how many point is a msec.
  # what you actually are counting is how many points there are between two msec
  # each msec step is not single point, but the space between two points (a small segment between two msec). For this reason you have to subtract one.
  x=(a-startmsec)*msecstep
  return(x+1)
  # notice that you return x+1. This is because the points in your vector goes from 1 to length of the vector.
  # when you are at point 1. you are at step 0 (i.e., no "small segment"). The maximum number of segment you can reach is lengthsegment-1.
  
}