## ItMLiHSmar2022
## standardise.R, child script
## Data standardisation, returns list
## Andreas Gammelgaard Damsbo, agdamsbo@clin.au.dk

standardise<-function(train,test,type){
  # From:
  # https://datascience.stackexchange.com/questions/13971/standardization-normalization-test-data-in-r
  
  sel<-sapply(Xtrain,is.numeric) # Deciding which to stadardise (only numeric)
  cnm<-colnames(Xtrain) # Saving column names for ordering
  
  # Subsetting
  
  ## Data to treat
  train.tr<-train[,sel]
  test.tr<-test[,sel]
  
  ## Data to save
  train.sv<-train[,!sel]
  test.sv<-test[,!sel]
  
  # Calculate mean and SD of train data
  trainMean <- sapply(train.tr,mean)
  trainSd <- sapply(train.tr,sd)
  
  if (type=="c"){
    ## centered
    norm.trainData<-sweep(train.tr, 2L, trainMean) # using the default "-" to subtract mean column-wise   
    norm.testData<-sweep(test.tr, 2L, trainMean) # using the default "-" to subtract mean column-wise   
  }
 
  if (type=="cs"){
    ## centered AND scaled (Z-score standardisation)
    norm.trainData<-sweep(sweep(train.tr, 2L, trainMean), 2, trainSd, "/")
    norm.testData<-sweep(sweep(test.tr, 2L, trainMean), 2, trainSd, "/")
  }
  return(list(XtrainSt=cbind(norm.trainData,train.sv)[,cnm], # Reordering columns to original
              XtestSt=cbind(norm.testData,test.sv)[,cnm]))
}