code: def test_ddof(self):
      pdf = pd.DataFrame(
          {
              "a": [1, 1, 1, 1, 2, 2, 2, 3, 3, 3] * 3,
              "b": [2, 3, 1, 4, 6, 9, 8, 10, 7, 5] * 3,
              "c": [3, 5, 2, 5, 1, 2, 6, 4, 3, 6] * 3,
          },
          index=np.random.rand(10 * 3),
      )
      psdf = ps.from_pandas(pdf)
  
      for ddof in [-1, 0, 1, 2, 3]:
          # std
          self.assert_eq(
              pdf.groupby("a").std(ddof=ddof).sort_index(),
              psdf.groupby("a").std(ddof=ddof).sort_index(),
              check_exact=False,
          )
          self.assert_eq(
              pdf.groupby("a")["b"].std(ddof=ddof).sort_index(),
              psdf.groupby("a")["b"].std(ddof=ddof).sort_index(),
              check_exact=False,
          )
          # var
          self.assert_eq(
              pdf.groupby("a").var(ddof=ddof).sort_index(),
              psdf.groupby("a").var(ddof=ddof).sort_index(),
              check_exact=False,
          )
          self.assert_eq(
              pdf.groupby("a")["b"].var(ddof=ddof).sort_index(),
              psdf.groupby("a")["b"].var(ddof=ddof).sort_index(),
              check_exact=False,
          )
          # sem
          self.assert_eq(
              pdf.groupby("a").sem(ddof=ddof).sort_index(),
              psdf.groupby("a").sem(ddof=ddof).sort_index(),
              check_exact=False,
          )
          self.assert_eq(
              pdf.groupby("a")["b"].sem(ddof=ddof).sort_index(),
              psdf.groupby("a")["b"].sem(ddof=ddof).sort_index(),
              check_exact=False,
          )
  
file_path: spark/python/pyspark/pandas/tests/groupby/test_stat_ddof.py
imports: import unittest
  import numpy
  import pandas
  from pyspark import pandas
  from pyspark.testing.pandasutils import PandasOnSparkTestCase
label_desc: Use image node_id 1 for calling the DdofTestsMixin obj's underlying member method code with example usage: obj.test_ddof() without return types