text: import unittest
  from pyalink.alink import *
  import numpy as np
  import pandas as pd
  class TestSampleStreamOp(unittest.TestCase):
      def test_samplestreamop(self):
  
          df_data = pd.DataFrame([
              ["-0.6264538 0.1836433"],
              ["-0.8356286 1.5952808"],
              ["0.3295078 -0.8204684"],
              ["0.4874291 0.7383247"],
              ["0.5757814 -0.3053884"],
              ["1.5117812 0.3898432"],
              ["-0.6212406 -2.2146999"],
              ["11.1249309 9.9550664"],
              ["9.9838097 10.9438362"],
              ["10.8212212 10.5939013"],
              ["10.9189774 10.7821363"],
              ["10.0745650 8.0106483"],
              ["10.6198257 9.9438713"],
              ["9.8442045 8.5292476"],
              ["9.5218499 10.4179416"],
          ])
          
          data = StreamOperator.fromDataframe(df_data, schemaStr='features string')
          
          sampleOp = SampleStreamOp().setRatio(0.3)
          
          data.link(sampleOp).print()
          
          StreamOperator.execute()
          pass