diff --git a/lib/youplot/dsv.rb b/lib/youplot/dsv.rb
index 2d7e751..b1d48fc 100644
--- a/lib/youplot/dsv.rb
+++ b/lib/youplot/dsv.rb
@@ -3,41 +3,49 @@
 require 'csv'
 
 module YouPlot
-  # Read and interpret Delimiter-separated values format file or stream.
+  # Module to handle DSV (Delimiter-separated values) format.
+  # Extract header and series.
   module DSV
     module_function
 
     def parse(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 if YouPlot.run_as_executable?
-        elsif h_size < s_size
-          warn "\e[35mThe number of headers is less than the number of series.\e[0m"
-          exit 1 if YouPlot.run_as_executable?
-        end
-      end
-    end
+      # Parse as CSV
+      arr = CSV.parse(input, col_sep: delimiter)
 
-    def parse_as_csv(input, delimiter)
-      CSV.parse(input, col_sep: delimiter)
-         .delete_if do |i|
-           i == [] or i.all? nil
-         end
+      # Remove blank lines
+      arr.delete_if do |i|
+        i == [] or i.all? nil
+      end
+
+      # get header
+      headers = get_headers(arr, headers, transpose)
+
+      # get series
+      series = get_series(arr, headers, transpose)
+
+      # Return if No header
+      return Data.new(headers, series) if headers.nil?
+
+      # Warn if header contains nil
+      warn "\e[35mHeaders contains nil in it.\e[0m" if headers.include?(nil)
+
+      # Warn if header contains ''
+      warn "\e[35mHeaders contains \"\" in it.\e[0m" if headers.include? ''
+
+      # Make sure the number of elements in the header matches the number of series.
+      h_size = headers.size
+      s_size = series.size
+
+      if h_size > s_size
+        warn "\e[35mThe number of headers is greater than the number of series.\e[0m"
+        exit 1 if YouPlot.run_as_executable?
+
+      elsif h_size < s_size
+        warn "\e[35mThe number of headers is less than the number of series.\e[0m"
+        exit 1 if YouPlot.run_as_executable?
+      end
+
+      Data.new(headers, series) if h_size == s_size
     end
 
     # Transpose different sized ruby arrays
@@ -47,31 +55,33 @@ module YouPlot
     end
 
     def get_headers(arr, headers, transpose)
-      if headers
-        if transpose
-          arr.map(&:first)
-        else
-          arr[0]
-        end
-      end
+      # header(-)
+      return nil unless headers
+
+      # header(+) trenspose(+)
+      return arr.map(&:first) if transpose
+
+      # header(+) transpose(-)
+      arr[0]
     end
 
     def get_series(arr, headers, transpose)
-      if headers
-        if arr.size > 1
-          if transpose
-            arr.map { |row| row[1..-1] }
-          else
-            transpose2(arr[1..-1])
-          end
-        else
-          Array.new(arr[0].size, [])
-        end
-      elsif transpose
-        arr
-      else
-        transpose2(arr)
+      # header(-)
+      unless headers
+        return arr if transpose
+
+        return transpose2(arr)
       end
+
+      # header(+) but no element in the series.
+      # TODO: should raise error?
+      return Array.new(arr[0].size, []) if arr.size == 1
+
+      # header(+) transpose(+)
+      return arr.map { |row| row[1..-1] } if transpose
+
+      # header(+) transpose(-)
+      transpose2(arr[1..-1])
     end
   end
 end