FreeMat
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Section: Array Generation and Manipulations
The shiftdim
function is used to shift the dimensions of an array. The general syntax for the shiftdim
function is
y = shiftdim(x,n)
where x
is a multidimensional array, and n
is an integer. If n
is a positive integer, then shiftdim
circularly shifts the dimensions of x
to the left, wrapping the dimensions around as necessary. If n
is a negative integer, then shiftdim
shifts the dimensions of x
to the right, introducing singleton dimensions as necessary. In its second form:
[y,n] = shiftdim(x)
the shiftdim
function will shift away (to the left) the leading singleton dimensions of x
until the leading dimension is not a singleton dimension (recall that a singleton dimension p
is one for which size(x,p) == 1
).
Here are some simple examples of using shiftdim
to remove the singleton dimensions of an array, and then restore them:
--> x = uint8(10*randn(1,1,1,3,2)); --> [y,n] = shiftdim(x); --> n ans = 3 --> size(y) ans = 3 2 --> c = shiftdim(y,-n); --> size(c) ans = 1 1 1 3 2 --> any(c~=x) ans = (:,:,1,1,1) = 0 (:,:,1,1,2) = 0
Note that these operations (where shifting involves only singleton dimensions) do not actually cause data to be resorted, only the size of the arrays change. This is not true for the following example, which triggers a call to permute
:
--> z = shiftdim(x,4);
Note that z
is now the transpose of x
--> squeeze(x) ans = 11 1 0 0 0 8 --> squeeze(z) ans = 11 0 0 1 0 8