Label Encoder functionality in R?

Question

In python, scikit has a great function called LabelEncoder that maps categorical levels (strings) to integer representation.

Is there anything in R to do this?

Answer 1

I wrote the following which I think works, the efficiency of which and/or how it will scale is not yet tested

str2Int.fit_transform<-function(df, plug_missing=TRUE){

  list_of_levels=list()  #empty list   

  #loop through the columns
  for (i in 1: ncol(df))
  {

    #only   
    if (is.character(df[,i]) ||  is.factor(df[,i]) ){

      #deal with missing
      if(plug_missing){

        #if factor
        if (is.factor(df[,i])){
          df[,i] = factor(df[,i], levels=c(levels(df[,i]), 'MISSING'))
          df[,i][is.na(df[,i])] = 'MISSING' 


        }else{   #if character

          df[,i][is.na(df[,i])] = 'MISSING' 

        }
      }#end missing IF

      levels<-unique(df[,i]) #distinct levels
      list_of_levels[[colnames(df)[i]]] <- levels #set list with name of the columns to the levels
      df[,i] <- as.numeric(factor(df[,i], levels = levels))

    }#end if character/factor IF


  }#end loop

  return (list(list_of_levels,df)) #return the list of levels and the new DF

}#end of function



str2Int.transform<-function(df,list_of_levels,plug_missing=TRUE)
{
  #loop through the columns
  for (i in 1: ncol(df))
  {

    #only   
    if (is.character(df[,i]) ||  is.factor(df[,i]) ){


      #deal with missing
      if(plug_missing){

        #if factor
        if (is.factor(df[,i])){
          df[,i] = factor(df[,i], levels=c(levels(df[,i]), 'MISSING'))
          df[,i][is.na(df[,i])] = 'MISSING' 


        }else{   #if character

          df[,i][is.na(df[,i])] = 'MISSING' 

        }
      }#end missing IF

      levels=list_of_levels[[colnames(df)[i]]]

      if (! is.null(levels)){
        df[,i] <- as.numeric(factor(df[,i], levels = levels))
      }

    }# character or factor

  }#end of loop

  return(df)

}#end of function




######################################################
# Test the functions
######################################################



###Test fit transform

# as strings
sample_dat <- data.frame(a_fact=c('Red','Blue','Blue',NA,'Green'), a_int=c(1,2,3,4,5), a_str=c('a','b','c','a','v'),stringsAsFactors=FALSE)

result<-str2Int.fit_transform(sample_dat)
result[[1]] #list of levels
result[[2]] #transformed df

#as factors
sample_dat <- data.frame(a_fact=c('Red','Blue','Blue',NA,'Green'), a_int=c(1,2,3,4,5), a_str=c('a','b','c','a','v'),stringsAsFactors=TRUE)

result<-str2Int.fit_transform(sample_dat)
result[[1]] #list of levels
result[[2]] #transformed df



###Test transform
str2Int.transform(sample_dat,result[[1]])