Improved error messages2

lib/uplot/plot.rb

@@ -128,10 +128,18 @@ module Uplot
       if series.size == 1
         warn "uplot: There is only one series of input data. Please check the delimiter."
         warn ""
+        warn "  Headers: \e[35m#{data.headers.inspect}\e[0m"
         warn "  The first item is: \e[35m\"#{series[0][0]}\"\e[0m"
         warn "  The last item is : \e[35m\"#{series[0][-1]}\"\e[0m"
         exit 1
       end
+      if fmt == 'xyxy' && series.size.odd?
+        warn "uplot: In the xyxy format, the number of series must be even."
+        warn ""
+        warn "  Number of series: \e[35m#{series.size}\e[0m"
+        warn "  Headers: \e[35m#{data.headers.inspect}\e[0m"
+        exit 1
+      end
     end
   end
 end