Rename Preprocessing to DSVReader

* DSV stands for Delimiter-separated values.
* Preprocessing is too vague.

lib/youplot/command.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require_relative 'preprocessing'
+require_relative 'dsv_reader'
 require_relative 'command/parser'
 
 # FIXME
@@ -55,9 +55,9 @@ module YouPlot
 
         @data = if @encoding
                   input2 = input.dup.force_encoding(@encoding).encode('utf-8')
-                  Preprocessing.input(input2, delimiter, headers, transpose)
+                  DSVReader.input(input2, delimiter, headers, transpose)
                 else
-                  Preprocessing.input(input, delimiter, headers, transpose)
+                  DSVReader.input(input, delimiter, headers, transpose)
                 end
 
         pp @data if @debug

lib/youplot/dsv_reader.rb

@@ -3,9 +3,10 @@
 require 'csv'
 
 module YouPlot
-  module Preprocessing
+  # Read and interpret Delimiter-separated values format file or stream.
+  module DSVReader
     module_function
-
+    
     def input(input, delimiter, headers, transpose)
       arr = parse_as_csv(input, delimiter)
       headers = get_headers(arr, headers, transpose)
@@ -68,19 +69,5 @@ module YouPlot
         transpose2(arr)
       end
     end
-
-    def count_values(arr)
-      # tally was added in Ruby 2.7
-      if Enumerable.method_defined? :tally
-        arr.tally
-      else
-        # https://github.com/marcandre/backports
-        arr.each_with_object(Hash.new(0)) { |item, res| res[item] += 1 }
-           .tap { |h| h.default = nil }
-      end
-        .sort { |a, b| a[1] <=> b[1] }
-        .reverse
-        .transpose
-    end
   end
 end