# Source code for mars.tensor.base.rollaxis

#!/usr/bin/env python
# -*- coding: utf-8 -*-
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#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
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import numpy as np
from ..utils import validate_axis
[docs]def rollaxis(tensor, axis, start=0):
"""
Roll the specified axis backwards, until it lies in a given position.
This function continues to be supported for backward compatibility, but you
should prefer `moveaxis`.
Parameters
----------
a : Tensor
Input tensor.
axis : int
The axis to roll backwards. The positions of the other axes do not
change relative to one another.
start : int, optional
The axis is rolled until it lies before this position. The default,
0, results in a "complete" roll.
Returns
-------
res : Tensor
a view of `a` is always returned.
See Also
--------
moveaxis : Move array axes to new positions.
roll : Roll the elements of an array by a number of positions along a
given axis.
Examples
--------
>>> import mars.tensor as mt
>>> a = mt.ones((3,4,5,6))
>>> mt.rollaxis(a, 3, 1).shape
(3, 6, 4, 5)
>>> mt.rollaxis(a, 2).shape
(5, 3, 4, 6)
>>> mt.rollaxis(a, 1, 4).shape
(3, 5, 6, 4)
"""
n = tensor.ndim
axis = validate_axis(n, axis)
if start < 0:
start += n
msg = "'%s' arg requires %d <= %s < %d, but %d was passed in"
if not (0 <= start < n + 1):
raise np.AxisError(msg % ("start", -n, "start", n + 1, start))
if axis < start:
# it's been removed
start -= 1
if axis == start:
return tensor
axes = list(range(0, n))
axes.remove(axis)
axes.insert(start, axis)
return tensor.transpose(axes)