BUG: IntervalIndex.unique() only contains the first interval if all interval borders are negative

[khemkaran10]

Fixes: #61917
Before FIx ❌:

idx_neg = pd.IntervalIndex.from_tuples([(-4, -3), (-4, -3), (-3, -2), (-3, -2), (-2, -1), (-2, -1)])
print(idx_neg.unique())

# Output:
# IntervalIndex([(-4, -3]], dtype='interval[int64, right]')

After Fix ✅:

idx_neg = pd.IntervalIndex.from_tuples([(-4, -3), (-4, -3), (-3, -2), (-3, -2), (-2, -1), (-2, -1)])
print(idx_neg.unique())

# output:
# IntervalIndex([(-4, -3], (-3, -2], (-2, -1]], dtype='interval[int64, right]')

• Fixes incorrect deduplication of negative-valued intervals when using .unique().

• Previously used .view("complex128"), which failed for negative floats/ints.

• closes BUG: IntervalIndex.unique() only contains the first interval if all interval borders are negative #61917

• Tests added and passed if fixing a bug or adding a new feature

• All code checks passed.

[il1sf4]

Hello @khemkaran10, I have tried your fix and I have the following issue. When i run with this branch this code:
import pandas as pd idx_neg = pd.IntervalIndex.from_tuples([(-4, -3), (-4, -3), (-3, -2), (-3, -2), (-2, -1), (-2, -1)]) print(idx_neg.unique())
I get from the last line: E ValueError: left side of interval must be <= right side
I have tried to debug the problem and I found that:
unique() from interval.py calls at the return self._from_combined(nc). the _from_combined() method from interval.py sets nc to nc = combined.view("i8").reshape(-1, 2). Here is the problem, because:
array([[-4.-3.j],
[-3.-2.j],
[-2.-1.j]])
gets transformed to:
array([[-4607182418800017408, -4609434218613702656],
[-4609434218613702656, -4611686018427387904],
[-4611686018427387904, -4616189618054758400]])
and then the method delivers an invalid Intervalindex, where left side is greater then the right side.

Gould you try to run the code again and assure, that idx_neg.unique() really returns "IntervalIndex([(-4, -3], (-3, -2], (-2, -1]], dtype='interval[int64, right]')"? In my tests the return is "IntervalIndex([([-4607182418800017408, -4609434218613702656], (-4609434218613702656, -4611686018427387904], (-4611686018427387904, -4616189618054758400]], dtype='interval[int64, right]')" which triggers the error: "E ValueError: left side of interval must be <= right side"

[khemkaran10]

@il1sf4 Thanks for pointing out. I have update the PR.

[jbrockmendel]

is the hstack really necessary here since the next 2 lines is just splitting them back up?

[khemkaran10]

thanks @jbrockmendel , It's not required. I'll change this.

[jbrockmendel]

if this is More Correct, should we just patch inside _combined directly? The only other place it is used is isin; will there be an analaguos but there?

[khemkaran10]

yes, agree we can add this logic directly in _combined.