Group elements in l by sign.
Behavior of sign:
Examples:
abjad> l = [0, 0, -1, -1, 2, 3, -5, 1, 2, 5, -5, -6]
abjad> generator = listtools.group_by_sign(l)
abjad> generator
<generator object at 0x118bf30>
abjad> list(generator)
[[0, 0], [-1, -1], [2, 3], [-5], [1, 2, 5], [-5, -6]]
abjad> generator = listtools.group_by_sign(l, sign = [-1])
abjad> generator
<generator object at 0x118f1e8>
abjad> list(generator)
[0, 0, [-1, -1], 2, 3, [-5], 1, 2, 5, [-5, -6]]
abjad> generator = listtools.group_by_sign(l, sign = [0])
abjad> generator
<generator object at 0x118f288>
abjad> list(generator)
[[0, 0], -1, -1, 2, 3, -5, 1, 2, 5, -5, -6]
abjad> generator = listtools.group_by_sign(l, sign = [1])
abjad> generator
<generator object at 0x118f2d8>
abjad> list(generator)
[0, 0, -1, -1, [2, 3], -5, [1, 2, 5], -5, -6]
abjad> generator = listtools.group_by_sign(l, sign = [-1, 0])
abjad> generator
<generator object at 0x118f350>
abjad> list(generator)
[[0, 0], [-1, -1], 2, 3, [-5], 1, 2, 5, [-5, -6]]
abjad> generator = listtools.group_by_sign(l, sign = [-1, 1])
abjad> generator
<generator object at 0x118f418>
abjad> list(generator)
[0, 0, [-1, -1], [2, 3], [-5], [1, 2, 5], [-5, -6]]
abjad> generator = listtools.group_by_sign(l, sign = [0, 1])
abjad> generator
<generator object at 0x118f508>
abjad> list(generator)
[[0, 0], -1, -1, [2, 3], -5, [1, 2, 5], -5, -6]
abjad> generator = listtools.group_by_sign(l, sign = [-1, 0, 1])
abjad> generator
<generator object at 0x118bf30>
abjad> list(generator)
[[0, 0], [-1, -1], [2, 3], [-5], [1, 2, 5], [-5, -6]]