import numpy as np
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from pandas import (
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DataFrame,
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Index,
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RangeIndex,
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Series,
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)
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import pandas._testing as tm
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# -----------------------------------------------------------------------------
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# Copy/view behaviour for the values that are set in a DataFrame
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def test_set_column_with_array():
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# Case: setting an array as a new column (df[col] = arr) copies that data
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df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
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arr = np.array([1, 2, 3], dtype="int64")
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df["c"] = arr
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# the array data is copied
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assert not np.shares_memory(df["c"].values, arr)
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# and thus modifying the array does not modify the DataFrame
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arr[0] = 0
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tm.assert_series_equal(df["c"], Series([1, 2, 3], name="c"))
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def test_set_column_with_series(using_copy_on_write):
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# Case: setting a series as a new column (df[col] = s) copies that data
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df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
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ser = Series([1, 2, 3])
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df["c"] = ser
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if using_copy_on_write:
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# TODO(CoW) with CoW we can delay the copy
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# assert np.shares_memory(df["c"].values, ser.values)
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assert not np.shares_memory(df["c"].values, ser.values)
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else:
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# the series data is copied
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assert not np.shares_memory(df["c"].values, ser.values)
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# and modifying the series does not modify the DataFrame
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ser.iloc[0] = 0
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assert ser.iloc[0] == 0
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tm.assert_series_equal(df["c"], Series([1, 2, 3], name="c"))
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def test_set_column_with_index(using_copy_on_write):
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# Case: setting an index as a new column (df[col] = idx) copies that data
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df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
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idx = Index([1, 2, 3])
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df["c"] = idx
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# the index data is copied
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assert not np.shares_memory(df["c"].values, idx.values)
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# and thus modifying the index does not modify the DataFrame
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idx.values[0] = 0
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tm.assert_series_equal(df["c"], Series([1, 2, 3], name="c"))
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idx = RangeIndex(1, 4)
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arr = idx.values
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df["d"] = idx
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assert not np.shares_memory(df["d"].values, arr)
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arr[0] = 0
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tm.assert_series_equal(df["d"], Series([1, 2, 3], name="d"))
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def test_set_columns_with_dataframe(using_copy_on_write):
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# Case: setting a DataFrame as new columns copies that data
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df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
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df2 = DataFrame({"c": [7, 8, 9], "d": [10, 11, 12]})
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df[["c", "d"]] = df2
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if using_copy_on_write:
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# TODO(CoW) with CoW we can delay the copy
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# assert np.shares_memory(df["c"].values, df2["c"].values)
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assert not np.shares_memory(df["c"].values, df2["c"].values)
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else:
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# the data is copied
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assert not np.shares_memory(df["c"].values, df2["c"].values)
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# and modifying the set DataFrame does not modify the original DataFrame
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df2.iloc[0, 0] = 0
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tm.assert_series_equal(df["c"], Series([7, 8, 9], name="c"))
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