Rename Preprocessing to DSVReader

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

lib/youplot/dsv_reader.rb

@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require 'csv'
+
+module YouPlot
+  # 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)
+      series = get_series(arr, headers, transpose)
+      if headers.nil?
+        Data.new(headers, series)
+      else
+        if headers.include?(nil)
+          warn "\e[35mHeaders contains nil in it.\e[0m"
+        elsif headers.include? ''
+          warn "\e[35mHeaders contains \"\" in it.\e[0m"
+        end
+        h_size = headers.size
+        s_size = series.size
+        if h_size == s_size
+          Data.new(headers, series)
+        elsif h_size > s_size
+          warn "\e[35mThe number of headers is greater than the number of series.\e[0m"
+          exit 1
+        elsif h_size < s_size
+          warn "\e[35mThe number of headers is less than the number of series.\e[0m"
+          exit 1
+        end
+      end
+    end
+
+    def parse_as_csv(input, delimiter)
+      CSV.parse(input, col_sep: delimiter)
+         .delete_if do |i|
+           i == [] or i.all? nil
+         end
+    end
+
+    # Transpose different sized ruby arrays
+    # https://stackoverflow.com/q/26016632
+    def transpose2(arr)
+      Array.new(arr.map(&:length).max) { |i| arr.map { |e| e[i] } }
+    end
+
+    def get_headers(arr, headers, transpose)
+      if headers
+        if transpose
+          arr.map(&:first)
+        else
+          arr[0]
+        end
+      end
+    end
+
+    def get_series(arr, headers, transpose)
+      if transpose
+        if headers
+          arr.map { |row| row[1..-1] }
+        else
+          arr
+        end
+      elsif headers
+        transpose2(arr[1..-1])
+      else
+        transpose2(arr)
+      end
+    end
+  end
+end