⚡️ Speed up method PandasMultiIndexingAdapter._repr_inline_ by 11%

[codeflash-ai]

📄 11% (0.11x) speedup for PandasMultiIndexingAdapter._repr_inline_ in xarray/core/indexing.py

⏱️ Runtime : 5.29 milliseconds → 4.75 milliseconds (best of 23 runs)

📝 Explanation and details

The optimized code achieves an 11% speedup through targeted micro-optimizations in two key areas:

1. Eliminated NumPy overhead for small arrays in format_array_flat:

• Replaced np.cumsum() with a simple Python loop that accumulates cumulative lengths directly
• Replaced np.argmax() with a next() generator expression to find the first index exceeding the threshold
• Used manual list building instead of zip_longest() + sum() for interleaving front/back items

These changes are effective because formatting operations typically deal with small arrays (dozens of items at most), where NumPy's overhead outweighs its vectorization benefits. Pure Python operations are faster for this scale.

2. Added fast path in _get_array_subset:

• When no subsetting is needed (array size ≤ threshold), directly return np.asarray(self) instead of going through concatenation and indexing logic
• This avoids unnecessary np.concatenate() and OuterIndexer operations for smaller arrays

Performance characteristics:

• The optimizations are most effective for typical display scenarios with small-to-medium sized arrays
• The changes preserve exact behavior while reducing function call overhead and temporary object creation
• The manual interleaving logic is more cache-friendly than iterator-based approaches for small lists

These optimizations target the common case where xarray displays array summaries in notebooks or console output, where arrays are usually formatted with just a few dozen elements visible.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	🔘 None Found
⏪ Replay Tests	✅ 6 Passed
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

⏪ Replay Tests and Runtime

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
test_pytest_xarrayteststest_concat_py_xarrayteststest_computation_py_xarrayteststest_formatting_py_xarray__replay_test_0.py::test_xarray_core_indexing_PandasMultiIndexingAdapter__repr_inline_	491μs	447μs	9.86%✅

To edit these changes git checkout codeflash/optimize-PandasMultiIndexingAdapter._repr_inline_-mja6q9gi and push.