import pytest
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from pandas import (
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DataFrame,
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Index,
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Series,
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)
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import pandas._testing as tm
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@pytest.mark.parametrize("n, frac", [(2, None), (None, 0.2)])
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def test_groupby_sample_balanced_groups_shape(n, frac):
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values = [1] * 10 + [2] * 10
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df = DataFrame({"a": values, "b": values})
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result = df.groupby("a").sample(n=n, frac=frac)
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values = [1] * 2 + [2] * 2
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expected = DataFrame({"a": values, "b": values}, index=result.index)
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tm.assert_frame_equal(result, expected)
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result = df.groupby("a")["b"].sample(n=n, frac=frac)
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expected = Series(values, name="b", index=result.index)
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tm.assert_series_equal(result, expected)
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def test_groupby_sample_unbalanced_groups_shape():
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values = [1] * 10 + [2] * 20
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df = DataFrame({"a": values, "b": values})
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result = df.groupby("a").sample(n=5)
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values = [1] * 5 + [2] * 5
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expected = DataFrame({"a": values, "b": values}, index=result.index)
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tm.assert_frame_equal(result, expected)
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result = df.groupby("a")["b"].sample(n=5)
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expected = Series(values, name="b", index=result.index)
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tm.assert_series_equal(result, expected)
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def test_groupby_sample_index_value_spans_groups():
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values = [1] * 3 + [2] * 3
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df = DataFrame({"a": values, "b": values}, index=[1, 2, 2, 2, 2, 2])
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result = df.groupby("a").sample(n=2)
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values = [1] * 2 + [2] * 2
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expected = DataFrame({"a": values, "b": values}, index=result.index)
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tm.assert_frame_equal(result, expected)
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result = df.groupby("a")["b"].sample(n=2)
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expected = Series(values, name="b", index=result.index)
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tm.assert_series_equal(result, expected)
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def test_groupby_sample_n_and_frac_raises():
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df = DataFrame({"a": [1, 2], "b": [1, 2]})
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msg = "Please enter a value for `frac` OR `n`, not both"
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with pytest.raises(ValueError, match=msg):
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df.groupby("a").sample(n=1, frac=1.0)
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with pytest.raises(ValueError, match=msg):
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df.groupby("a")["b"].sample(n=1, frac=1.0)
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def test_groupby_sample_frac_gt_one_without_replacement_raises():
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df = DataFrame({"a": [1, 2], "b": [1, 2]})
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msg = "Replace has to be set to `True` when upsampling the population `frac` > 1."
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with pytest.raises(ValueError, match=msg):
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df.groupby("a").sample(frac=1.5, replace=False)
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with pytest.raises(ValueError, match=msg):
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df.groupby("a")["b"].sample(frac=1.5, replace=False)
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@pytest.mark.parametrize("n", [-1, 1.5])
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def test_groupby_sample_invalid_n_raises(n):
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df = DataFrame({"a": [1, 2], "b": [1, 2]})
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if n < 0:
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msg = "A negative number of rows requested. Please provide `n` >= 0."
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else:
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msg = "Only integers accepted as `n` values"
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with pytest.raises(ValueError, match=msg):
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df.groupby("a").sample(n=n)
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with pytest.raises(ValueError, match=msg):
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df.groupby("a")["b"].sample(n=n)
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def test_groupby_sample_oversample():
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values = [1] * 10 + [2] * 10
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df = DataFrame({"a": values, "b": values})
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result = df.groupby("a").sample(frac=2.0, replace=True)
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values = [1] * 20 + [2] * 20
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expected = DataFrame({"a": values, "b": values}, index=result.index)
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tm.assert_frame_equal(result, expected)
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result = df.groupby("a")["b"].sample(frac=2.0, replace=True)
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expected = Series(values, name="b", index=result.index)
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tm.assert_series_equal(result, expected)
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def test_groupby_sample_without_n_or_frac():
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values = [1] * 10 + [2] * 10
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df = DataFrame({"a": values, "b": values})
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result = df.groupby("a").sample(n=None, frac=None)
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expected = DataFrame({"a": [1, 2], "b": [1, 2]}, index=result.index)
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tm.assert_frame_equal(result, expected)
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result = df.groupby("a")["b"].sample(n=None, frac=None)
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expected = Series([1, 2], name="b", index=result.index)
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tm.assert_series_equal(result, expected)
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@pytest.mark.parametrize(
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"index, expected_index",
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[(["w", "x", "y", "z"], ["w", "w", "y", "y"]), ([3, 4, 5, 6], [3, 3, 5, 5])],
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)
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def test_groupby_sample_with_weights(index, expected_index):
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# GH 39927 - tests for integer index needed
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values = [1] * 2 + [2] * 2
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df = DataFrame({"a": values, "b": values}, index=Index(index))
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result = df.groupby("a").sample(n=2, replace=True, weights=[1, 0, 1, 0])
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expected = DataFrame({"a": values, "b": values}, index=Index(expected_index))
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tm.assert_frame_equal(result, expected)
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result = df.groupby("a")["b"].sample(n=2, replace=True, weights=[1, 0, 1, 0])
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expected = Series(values, name="b", index=Index(expected_index))
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tm.assert_series_equal(result, expected)
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def test_groupby_sample_with_selections():
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# GH 39928
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values = [1] * 10 + [2] * 10
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df = DataFrame({"a": values, "b": values, "c": values})
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result = df.groupby("a")[["b", "c"]].sample(n=None, frac=None)
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expected = DataFrame({"b": [1, 2], "c": [1, 2]}, index=result.index)
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tm.assert_frame_equal(result, expected)
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def test_groupby_sample_with_empty_inputs():
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# GH48459
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df = DataFrame({"a": [], "b": []})
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groupby_df = df.groupby("a")
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result = groupby_df.sample()
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expected = df
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tm.assert_frame_equal(result, expected)
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