8000 MAINT/BUG: Remove special-casing for 0d arrays, now that indexing with a single boolean is ok by eric-wieser · Pull Request #9900 · numpy/numpy · GitHub
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MAINT/BUG: Remove special-casing for 0d arrays, now that indexing with a single boolean is ok #9900

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Merged
merged 4 commits into from
Oct 24, 2017
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MAINT/BUG: Remove special-casing for 0d arrays, now that indexing with a single boolean is ok #9900

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4712875
MAINT/BUG: Remove special-casing for 0d arrays, now that indexing wit…
eric-wieser Oct 21, 2017
4729550
DOC: piecewise callables take 1d arrays
eric-wieser Oct 21, 2017
303941c
TST: Add test for 0d conditions in np.piecewise
eric-wieser Oct 22, 2017
c875b13
BUG: Throw an error if too many functions are given to piecewise
eric-wieser Oct 22, 2017
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34 changes: 16 additions & 18 deletions numpy/lib/function_base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1254,12 +1254,12 @@ def piecewise(x, condlist, funclist, *args, **kw):

The length of `condlist` must correspond to that of `funclist`.
If one extra function is given, i.e. if
``len(funclist) - len(condlist) == 1``, then that extra function
``len(funclist) == len(condlist) + 1``, then that extra function
is the default value, used wherever all conditions are false.
funclist : list of callables, f(x,*args,**kw), or scalars
Each function is evaluated over `x` wherever its corresponding
condition is True. It should take an array as input and give an array
or a scalar value as output. If, instead of a callable,
condition is True. It should take a 1d array as input and give an 1d
array or a scalar value as output. If, instead of a callable,
a scalar is provided then a constant function (``lambda x: scalar``) is
assumed.
args : tuple, optional
Expand Down Expand Up @@ -1323,25 +1323,24 @@ def piecewise(x, condlist, funclist, *args, **kw):
"""
x = asanyarray(x)
n2 = len(funclist)
if (isscalar(condlist) or not (isinstance(condlist[0], list) or
isinstance(condlist[0], ndarray))):
if not isscalar(condlist) and x.size == 1 and x.ndim == 0:
condlist = [[c] for c in condlist]
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@eric-wieser eric-wieser Oct 21, 2017 •
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This line inserts an extra dim into cond to match what we to did to 0d x below - so is no longer needed.

Note that this would misfire on non-0d x sometimes - which is why a test below needed changing

Essentially, this line is replaced with pass, and then the nested ifs are collapsed

else:
condlist = [condlist]

# undocumented: single condition is promoted to a list of one condition
if isscalar(condlist) or (
not isinstance(condlist[0], (list, ndarray)) and x.ndim != 0):
condlist = [condlist]

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So, was the idea to deprecate this? An alternative might be to just add ndmin=1 in the conversion to boolean array below.

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I'd like to deprecate this in future, but this patch is orthogonal to that

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ndim=1 won't help - this is intended to also promote 1d arrays to a list of length 1 containing a single 1d array.

condlist = array(condlist, dtype=bool)
n = len(condlist)
# This is a hack to work around problems with NumPy's
# handling of 0-d arrays and boolean indexing with
# numpy.bool_ scalars
zerod = False
if x.ndim == 0:
x = x[None]
zerod = True
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I think this worked around arr_0d[bool_0d] not being supported in the past


if n == n2 - 1: # compute the "otherwise" condition.
condelse = ~np.any(condlist, axis=0, keepdims=True)
condlist = np.concatenate([condlist, condelse], axis=0)
n += 1
elif n != n2:
raise ValueError(
"with {} condition(s), either {} or {} functions are expected"
.format(n, n, n+1)
)

y = zeros(x.shape, x.dtype)
for k in range(n):
Expand All @@ -1352,8 +1351,7 @@ def piecewise(x, condlist, funclist, *args, **kw):
vals = x[condlist[k]]
if vals.size > 0:
y[condlist[k]] = item(vals, *args, **kw)
if zerod:
y = y.squeeze()

return y


Expand Down
18 changes: 17 additions & 1 deletion numpy/lib/tests/test_function_base.py
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Expand Up @@ -2514,6 +2514,11 @@ def test_simple(self):
x = piecewise([0, 0], [[False, True]], [lambda x:-1])
assert_array_equal(x, [0, -1])

assert_raises_regex(ValueError, '1 or 2 functions are expected',
piecewise, [0, 0], [[False, True]], [])
assert_raises_regex(ValueError, '1 or 2 functions are expected',
piecewise, [0, 0], [[False, True]], [1, 2, 3])

def test_two_conditions(self):
x = piecewise([1, 2], [[True, False], [False, True]], [3, 4])
assert_array_equal(x, [3, 4])
Expand All @@ -2538,7 +2543,7 @@ def test_0d(self):
assert_(y == 0)

x = 5
y = piecewise(x, [[True], [False]], [1, 0])
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@eric-wieser eric-wieser Oct 21, 2017 •
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This didn't make any sense, and should have failed. The conditions should be the same shape as the x. We got away with it because the 0d special-casing made the shapes match.

y = piecewise(x, [True, False], [1, 0])
assert_(y.ndim == 0)
assert_(y == 1)

Expand All @@ -2556,6 +2561,17 @@ def test_0d_comparison(self):
y = piecewise(x, [x <= 3, (x > 3) * (x <= 5), x > 5], [1, 2, 3])
assert_array_equal(y, 2)

assert_raises_regex(ValueError, '2 or 3 functions are expected',
piecewise, x, [x <= 3, x > 3], [1])
assert_raises_regex(ValueError, '2 or 3 functions are expected',
piecewise, x, [x <= 3, x > 3], [1, 1, 1, 1])

def test_0d_0d_condition(self):
x = np.array(3)
c = np.array(x > 3)
y = piecewise(x, [c], [1, 2])
assert_equal(y, 2)

def test_multidimensional_extrafunc(self):
x = np.array([[-2.5, -1.5, -0.5],
[0.5, 1.5, 2.5]])
Expand Down
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