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Add scalar comparison operators for DataArray and Dataset #3782

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Copilot AI commented Oct 28, 2025 •
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Variable supports comparison with scalar numbers (sc.scalar(2) == 2), but DataArray and Dataset return False instead of performing element-wise comparison. This inconsistency breaks the expected behavior where sc.DataArray(sc.scalar(2)) == 2 should return a DataArray with boolean result.

Changes

lib/python/dataset.cpp

  • Added bind_comparison_scalars(c) to DataArray bindings (line 111)
  • Added comparison bindings for Dataset (lines 280-283): bind_comparison<Dataset>, bind_comparison<DataArray>, bind_comparison<Variable>, and bind_comparison_scalars

tests/core/comparison_test.py

  • Added test coverage for DataArray and Dataset comparison operators (==, !=, <, <=, >, >=) with scalar numbers

Example

import scipp as sc

# Before: returns False
# After: returns DataArray with data=Variable(True)
sc.DataArray(sc.scalar(2)) == 2

# Before: returns False  
# After: returns Dataset with 'a': DataArray with data=Variable(True)
sc.Dataset({'a': sc.scalar(2)}) == 2

The implementation converts scalars to Variables via the existing bind_comparison_scalars mechanism, then uses the already-supported Variable comparison operators.

Original prompt

This section details on the original issue you should resolve

<issue_title>Inconsistent eq for variable and data array with number</issue_title>
<issue_description>The equality comparison operator behaves differently for variables and data arrays:

import scipp as sc

print(sc.scalar(2) == 2)
# <scipp.Variable> ()       bool        <no unit>  True

print(sc.DataArray(sc.scalar(2)) == 2)
# False

print(sc.Dataset({'a': sc.scalar(2)}) == 2)
# False

print((sc.DataGroup({'a': sc.scalar(2)}) == 2)['a'])
# <scipp.Variable> ()       bool        <no unit>  True

I would expect the 2nd and 3rd example to work like the first. Especially, since sc.DataArray(sc.scalar(2)) == sc.scalar(2) returns a data array containing True.

Looking at the code, I think we are simply missing some overloads.</issue_description>

Comments on the Issue (you are @copilot in this section)

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Copilot AI and others added 3 commits October 28, 2025 18:31
@MridulS
Add scalar comparison bindings for DataArray and Dataset
c069af4 
Co-authored-by: MridulS <5363860+MridulS@users.noreply.github.com>
@MridulS
Fix trailing whitespace in test file
10f1d94 
Co-authored-by: MridulS <5363860+MridulS@users.noreply.github.com>
@MridulS
Final implementation complete
d25ebfb 
Co-authored-by: MridulS <5363860+MridulS@users.noreply.github.com>
Copilot AI changed the title [WIP] Fix inconsistent __eq__ behavior for variable and data array Add scalar comparison operators for DataArray and Dataset Oct 28, 2025
Copilot AI requested a review from MridulS October 28, 2025 18:42
@jl-wynen jl-wynen mentioned this pull request Dec 11, 2025
Merged
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Inconsistent __eq__ for variable and data array with number

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@MridulS