BUG: signal.detrend on main no longer accepts a sequence for bp

[jakevdp]

Describe your issue.

Passing a sequence of integers to the bp argument of scipy.signal.detrend results in an error on the main branch. This appears to be due to #18455, which is not yet part of any release or pre-release (see #18455 (comment))

Reproducing Code Example

import scipy
import numpy as np
rng = np.random.RandomState(12345)

x = rng.rand(10)
bp = np.array([0, 2])

scipy.signal.detrend(x, bp=bp)

Error message

/usr/local/lib/python3.10/dist-packages/numpy/lib/arraysetops.py:270: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray.
  ar = np.asanyarray(ar)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
[<ipython-input-9-3498418e6fd9>](https://localhost:8080/#) in <cell line: 8>()
      7 
----> 8 print(scipy.signal.detrend(x, bp=bp)

[/usr/local/lib/python3.10/dist-packages/scipy/signal/_signaltools.py](https://localhost:8080/#) in detrend(data, axis, type, bp, overwrite_data)
   3561         dshape = data.shape
   3562         N = dshape[axis]
-> 3563         bp = np.sort(np.unique([0, bp, N]))
   3564         if np.any(bp > N):
   3565             raise ValueError("Breakpoints must be less than length "

/usr/local/lib/python3.10/dist-packages/numpy/core/overrides.py in unique(*args, **kwargs)

[/usr/local/lib/python3.10/dist-packages/numpy/lib/arraysetops.py](https://localhost:8080/#) in unique(ar, return_index, return_inverse, return_counts, axis)
    270     ar = np.asanyarray(ar)
    271     if axis is None:
--> 272         ret = _unique1d(ar, return_index, return_inverse, return_counts)
    273         return _unpack_tuple(ret)
    274 

[/usr/local/lib/python3.10/dist-packages/numpy/lib/arraysetops.py](https://localhost:8080/#) in _unique1d(ar, return_index, return_inverse, return_counts)
    331         aux = ar[perm]
    332     else:
--> 333         ar.sort()
    334         aux = ar
    335     mask = np.empty(aux.shape, dtype=np.bool_)

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

SciPy/NumPy/Python version and system information

1.11.0.dev0+2112.00f4e2e 1.22.4 sys.version_info(major=3, minor=10, micro=12, releaselevel='final', serial=0)
Build Dependencies:
  blas:
    detection method: pkgconfig
    found: true
    include directory: /usr/local/include
    lib directory: /usr/local/lib
    name: openblas
    openblas configuration: USE_64BITINT= DYNAMIC_ARCH=1 DYNAMIC_OLDER= NO_CBLAS=
      NO_LAPACK= NO_LAPACKE= NO_AFFINITY=1 USE_OPENMP= HASWELL MAX_THREADS=2
    pc file directory: /usr/local/lib/pkgconfig
    version: 0.3.21.dev
  lapack:
    detection method: pkgconfig
    found: true
    include directory: /usr/local/include
    lib directory: /usr/local/lib
    name: openblas
    openblas configuration: USE_64BITINT= DYNAMIC_ARCH=1 DYNAMIC_OLDER= NO_CBLAS=
      NO_LAPACK= NO_LAPACKE= NO_AFFINITY=1 USE_OPENMP= HASWELL MAX_THREADS=2
    pc file directory: /usr/local/lib/pkgconfig
    version: 0.3.21.dev
  pybind11:
    detection method: config-tool
    include directory: unknown
    name: pybind11
    version: 2.10.4
Compilers:
  c:
    commands: cc
    linker: ld.bfd
    name: gcc
    version: 10.2.1
  c++:
    commands: c++
    linker: ld.bfd
    name: gcc
    version: 10.2.1
  cython:
    commands: cython
    linker: cython
    name: cython
    version: 0.29.34
  fortran:
    commands: gfortran
    linker: ld.bfd
    name: gcc
    version: 10.2.1
  pythran:
    include directory: ../../tmp/pip-build-env-qaptfljs/overlay/lib/python3.10/site-packages/pythran
    version: 0.13.1
Machine Information:
  build:
    cpu: x86_64
    endian: little
    family: x86_64
    system: linux
  cross-compiled: false
  host:
    cpu: x86_64
    endian: little
    family: x86_64
    system: linux
Python Information:
  path: /opt/python/cp310-cp310/bin/python
  version: '3.10'

[andyfaff]

Fyi the location for nightly builds is now https://pypi.anaconda.org/scientific-python-nightly-wheels/simple

[ev-br]

So it's the first glitch of the array-api compat movement: array API does not have np.r_ .

In [5]: np.unique(np.r_[0, bp, 10])
Out[5]: array([ 0,  2, 10])

In [6]: np.unique([0, bp, 10])
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[6], line 1
----> 1 np.unique([0, bp, 10])

File <__array_function__ internals>:200, in unique(*args, **kwargs)

File ~/mambaforge/envs/scipy-dev/lib/python3.10/site-packages/numpy/lib/arraysetops.py:272, in unique(ar, return_index, return_inverse, return_counts, axis, equal_nan)
    138 @array_function_dispatch(_unique_dispatcher)
    139 def unique(ar, return_index=False, return_inverse=False,
    140            return_counts=False, axis=None, *, equal_nan=True):
    141     """
    142     Find the unique elements of an array.
    143 
   (...)
    270 
    271     """
--> 272     ar = np.asanyarray(ar)
    273     if axis is None:
    274         ret = _unique1d(ar, return_index, return_inverse, return_counts, 
    275                         equal_nan=equal_nan)

ValueError: setting an array element with a sequence. The requested array has an inhomogeneous shape after 1 dimensions. The detected shape was (3,) + inhomogeneous part.

A fix is (untested) --- so np.r_ is ugly, huh :-).

In [27]: np.sort(np.unique(np.concatenate(([0], bp, [10]))))
Out[27]: array([ 0,  2, 10])

[jakevdp]

It needs to handle scalar inputs for bp as well, so possibly normalize with bp = np.atleast_1d(bp) before doing that concatenation

[ev-br]

Yes thanks, #18676 does it. Could you test that one Jake? The test suite for detrend is very minimal and was even more minimal until the 1.11 cycle. I wouldn't be surprised if there are more issues.