7f827147d1
You can preview this rule [here](https://sonarsource.github.io/rspec/#/rspec/S6729/python) (updated a few minutes after each push). ## Review A dedicated reviewer checked the rule description successfully for: - [ ] logical errors and incorrect information - [ ] information gaps and missing content - [ ] text style and tone - [ ] PR summary and labels follow [the guidelines](https://github.com/SonarSource/rspec/#to-modify-an-existing-rule) --------- Co-authored-by: joke1196 <joke1196@users.noreply.github.com> Co-authored-by: David Kunzmann <david.kunzmann@sonarsource.com>
82 lines
2.8 KiB
Plaintext
82 lines
2.8 KiB
Plaintext
This rule raises an issue when ``++np.where++`` is used with only the condition parameter set.
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== Why is this an issue?
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The NumPy function ``++np.where++`` provides a way to execute operations on an array under a certain condition:
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[source,python]
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----
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import numpy as np
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arr = np.array([1,2,3,4])
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result = np.where(arr > 3, arr * 2, arr)
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----
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In the example above the ``++np.where++`` function will multiply all the elements in the array which satisfy the condition: ``++element > 3++`` by 2.
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The elements that do not satisfy the condition will be left untouched.
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The ``++result++`` array holds now the values 1, 2, 3 and 8.
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It is also possible to call ``++np.where++`` with only the condition parameter set:
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[source,python]
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----
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import numpy as np
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arr = np.array([1,2,3,4])
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result = np.where(arr > 2)
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----
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Even though this is perfectly valid code in NumPy, it may not yield the expected results.
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When providing only the condition parameter to the ``++np.where++`` function, it will behave as ``++np.asarray(condition).nonzero()++`` or ``++np.nonzero(condition)++``.
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Both these functions provide a way to find the indices of the elements satisfying the condition passed as parameter.
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Be mindful that ``++np.asarray(condition).nonzero()++`` and ``++np.nonzero(condition)++`` do not return the *values* that satisfy the condition but only their *indices*.
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This means the ``++result++`` variable now holds a tuple
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with the first element being an array of all the indices where the condition ``++arr > 2++`` was satisfied: ``++(array([2,3]),)++``.
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If the intention is to find the indices of the elements which satisfy a certain condition it is preferable to use the ``++np.asarray(condition).nonzero()++`` or ``++np.nonzero(condition)++`` function instead.
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== How to fix it
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To fix this issue either:
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* provide all three parameters to the ``++np.where++`` function (condition, value if the condition is satisfied, value if the condition is not satisfied) or,
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* use the ``++np.nonzero++`` function.
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=== Code examples
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==== Noncompliant code example
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[source,text,diff-id=1,diff-type=noncompliant]
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----
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import numpy as np
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def bigger_than_two():
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arr = np.array([1,2,3,4])
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result = np.where(arr > 2) # Noncompliant: only the condition parameter is provided to the np.where function.
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----
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==== Compliant solution
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[source,text,diff-id=1,diff-type=compliant]
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----
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import numpy as np
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def bigger_than_two():
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arr = np.array([1,2,3,4])
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result = np.where(arr > 2, arr + 1, arr) # Compliant
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indices = np.nonzero(arr > 2) # Compliant
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----
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== Resources
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=== Documentation
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* NumPy Documentation - https://numpy.org/doc/stable/reference/generated/numpy.where.html#numpy-where[numpy.where]
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* NumPy Documentation - https://numpy.org/doc/stable/reference/generated/numpy.nonzero.html#numpy.nonzero[numpy.nonzero]
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