def unravel_index(x,dims):
"""Convert a flat index into an index tuple for an array of given shape.
e.g. for a 2x2 array, unravel_index(2,(2,2)) returns (1,0).
Example usage:
p = x.argmax()
idx = unravel_index(p,x.shape)
x[idx] == x.max()
Note: x.flat[p] == x.max()
Thus, it may be easier to use flattened indexing than to re-map
the index to a tuple.
"""
if x > _nx.prod(dims)-1 or x < 0:
raise ValueError("Invalid index, must be 0 <= x <= number of elements.")
idx = _nx.empty_like(dims)
# Take dimensions
# [a,b,c,d]
# Reverse and drop first element
# [d,c,b]
# Prepend [1]
# [1,d,c,b]
# Calculate cumulative product
# [1,d,dc,dcb]
# Reverse
# [dcb,dc,d,1]
dim_prod = _nx.cumprod([1] + list(dims)[:0:-1])[::-1]
# Indeces become [x/dcb % a, x/dc % b, x/d % c, x/1 % d]
return tuple(x/dim_prod % dims)
def unravel_index(x,dims):
"""Convert a flat index into an index tuple for an array of given shape.
e.g. for a 2x2 array, unravel_index(2,(2,2)) returns (1,0).
Example usage:
p = x.argmax()
idx = unravel_index(p,x.shape)
x[idx] == x.max()
Note: x.flat[p] == x.max()
Thus, it may be easier to use flattened indexing than to re-map
the index to a tuple.
"""
if x > _nx.prod(dims)-1 or x < 0:
raise ValueError("Invalid index, must be 0 <= x <= number of elements.")
idx = _nx.empty_like(dims)
# Take dimensions
# [a,b,c,d]
# Reverse and drop first element
# [d,c,b]
# Prepend [1]
# [1,d,c,b]
# Calculate cumulative product
# [1,d,dc,dcb]
# Reverse
# [dcb,dc,d,1]
dim_prod = _nx.cumprod([1] + list(dims)[:0:-1])[::-1]
# Indices become [x/dcb % a, x/dc % b, x/d % c, x/1 % d]
return tuple(x/dim_prod % dims)
def unravel_index(x, dims):
"""
Convert a flat index to an index tuple for an array of given shape.
Parameters
----------
x : int
Flattened index.
dims : tuple of ints
Input shape, the shape of an array into which indexing is
required.
Returns
-------
idx : tuple of ints
Tuple of the same shape as `dims`, containing the unraveled index.
Notes
-----
In the Examples section, since ``arr.flat[x] == arr.max()`` it may be
easier to use flattened indexing than to re-map the index to a tuple.
Examples
--------
>>> arr = np.arange(20).reshape(5, 4)
>>> arr
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11],
[12, 13, 14, 15],
[16, 17, 18, 19]])
>>> x = arr.argmax()
>>> x
19
>>> dims = arr.shape
>>> idx = np.unravel_index(x, dims)
>>> idx
(4, 3)
>>> arr[idx] == arr.max()
True
"""
if x > _nx.prod(dims) - 1 or x < 0:
raise ValueError("Invalid index, must be 0 <= x <= number of elements.")
idx = _nx.empty_like(dims)
# Take dimensions
# [a,b,c,d]
# Reverse and drop first element
# [d,c,b]
# Prepend [1]
# [1,d,c,b]
# Calculate cumulative product
# [1,d,dc,dcb]
# Reverse
# [dcb,dc,d,1]
dim_prod = _nx.cumprod([1] + list(dims)[:0:-1])[::-1]
# Indices become [x/dcb % a, x/dc % b, x/d % c, x/1 % d]
return tuple(x / dim_prod % dims)
def unravel_index(x, dims):
"""
Convert a flat index into an index tuple for an array of given shape.
Parameters
----------
x : int
Flattened index.
dims : shape tuple
Input shape.
Notes
-----
In the Examples section, since ``arr.flat[x] == arr.max()`` it may be
easier to use flattened indexing than to re-map the index to a tuple.
Examples
--------
>>> arr = np.ones((5,4))
>>> arr
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11],
[12, 13, 14, 15],
[16, 17, 18, 19]])
>>> x = arr.argmax()
>>> x
19
>>> dims = arr.shape
>>> idx = np.unravel_index(x, dims)
>>> idx
(4, 3)
>>> arr[idx] == arr.max()
True
"""
if x > _nx.prod(dims) - 1 or x < 0:
raise ValueError(
"Invalid index, must be 0 <= x <= number of elements.")
idx = _nx.empty_like(dims)
# Take dimensions
# [a,b,c,d]
# Reverse and drop first element
# [d,c,b]
# Prepend [1]
# [1,d,c,b]
# Calculate cumulative product
# [1,d,dc,dcb]
# Reverse
# [dcb,dc,d,1]
dim_prod = _nx.cumprod([1] + list(dims)[:0:-1])[::-1]
# Indices become [x/dcb % a, x/dc % b, x/d % c, x/1 % d]
return tuple(x / dim_prod % dims)
