| by.trackdata | R Documentation | 
A given function 'FUN' is applied to the data corresponding to each segment of data.
## S3 method for class 'trackdata'
by(data, INDICES = NULL, FUN, ..., simplify = FALSE)
| data | a track data object | 
| INDICES | a list of segment indices, like a label vector | 
| FUN | a function that is applied to each segment | 
| ... | arguments of the function fun | 
| simplify | simplify = TRUE , output is a matrix; simplify = FALSE a list is returned | 
It is the same as trapply but with the extension to subsume calculation to groups of segments. Note, if you do not want to apply the function fun to a special group of segments, use trapply instead.
list or vector
Jonathan Harrington
trapply, by, trackdata
dapply smooth apply
  data(demo.vowels)
  data(demo.vowels.fm)
   #mean F1 subsumed for each vowel
   ################################
   lab = label(demo.vowels)
   by(demo.vowels.fm[,1], lab ,sapply,mean,simplify=FALSE)
   #mean F1 subsumed for segment onsets mids and offsets
   ##############################################
   data = demo.vowels.fm
   llabs = NULL
   for (ind in 1:dim(data$ftime)[1]) {
     seglabs = rep("mid",data$index[ind,2]-data$index[ind,1]+1)
     seglabs[1] = "on"
     seglabs[length(seglabs)] = "off"
     llabs = as.vector(c(llabs , seglabs))
   }
   by(demo.vowels.fm[,1], llabs , sapply, mean , simplify=FALSE)
   #mean F1 subsumed for segment onsets mids and offsets subsumed for each vowel
   #####################################################################
   by(demo.vowels.fm[,1], list(lab = lab, llabs = llabs) , sapply, mean , simplify=FALSE)
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