1 files changed, 61 insertions, 3 deletions

diff --git a/R/preprocess.R b/R/preprocess.R
index 66c4a67..07b0a4a 100644
--- a/R/preprocess.R
+++ b/R/preprocess.R
@@ -1,6 +1,6 @@
-#' Remove linear trends
+#' Remove offsets and linear trends
 #' 
-#' Removes the mean value or linear trends in each of the input and output matrices. 
+#' Removes the offsets or linear trends in each of the input and output matrices. 
 #' 
 #' @param data an object of class \code{idframe}
 #' @param type trend type - "constant" or "linear". (Default: \code{"linear"})
@@ -21,7 +21,7 @@
 #' fit <- detrend(cstr) # remove linear trends 
 #' Zdetrend <- predict(fit) # get the detrended data
 #' 
-#' demean <- detrend(cstr,type="constant") # remove mean values
+#' demean <- detrend(cstr,type="constant") # remove offsets
 #' Zcent <- predict(demean) # get the centered data
 #' 
 #' @seealso \code{\link{predict.detrend}}, \code{\link[stats]{lm}}
@@ -125,4 +125,62 @@ misdata <- function(data){
                      end=data$t.end,Ts= data$Ts))
   
   return(dataout)
+}
+
+#' Subset or Resample idframe data
+#' 
+#' \code{dataSlice} is a subsetting method for objects of class \code{idframe}. It 
+#' extracts the subset of the object \code{data} observed between indices \code{start}
+#' and \code{end}.  If a frequency is specified, the series is then re-sampled at the 
+#' new frequency.
+#' 
+#' @param data an object of class \code{idframe}
+#' @param start the start index
+#' @param end the end index
+#' @param freq the new sampling frequency
+#' 
+#' @details
+#' The dataSlice function extends the \code{\link[stats]{window}} function for idframe
+#' objects
+#' 
+#' @return an idframe object
+#' 
+#' @examples
+#' data(cstr)
+#' cstrsub <- dataSlice(cstr,start=200,end=400) # extract between indices 200 and 400
+#' cstrTrain <- dataSlice(cstr,end=4500) # extract upto index 4500
+#' cstrTest <- dataSlice(cstr,start=6501) # extract from index 6501 till the end
+#' cstr_new <- dataSlice(cstr,freq=3) # resample data at thrice the frequency  
+#' 
+#' @seealso \code{\link[stats]{window}}
+#' @export
+dataSlice <- function(data,start=NULL,end=NULL,freq=NULL){
+  # check if the class is correct
+  if(class(data)!='idframe')
+    stop("Not an idframe data")
+  
+  nin <- dim(data$input)[2]; nout <- dim(data$output)[2]
+  dataMatrix <- cbind(data$input,data$output)
+  if(data$type=="freq"){
+    dataMatrix <- cbind(dataMatrix,data$frequencies)
+  } else {
+    timeSeq <- seq(from=data$t.start,to=data$t.end,by=data$Ts)
+    dataMatrix <- cbind(dataMatrix,timeSeq)
+  }
+  
+  l <- as.list(dataMatrix)
+  trimData <- as.data.frame(sapply(l,window,start=start,end=end,deltat=freq))
+  
+  trim <- idframe(output=trimData[,(nin+1):(nin+nout),drop=F],
+                  input=trimData[,1:nin,drop=F],type=data$type,Ts=data$Ts,
+                  tUnit=data$tUnit)
+  
+  if(trim$type=="freq"){
+    trim$frequncies <- trimData[,ncol(trimData)]
+  } else {
+    trim$t.start <- trimData[1,ncol(trimData)]
+    trim$t.end <- trimData[nrow(trimData),ncol(trimData)]
+  }
+  
+  return(trim)
 }
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