shiftdim

Shift array dimensions

Usage

shiftdim(A, k)

• A should be an array and k should be a real integer scalar not equal to Inf nor NaN. It shifts the size vector of A k times.
• If k is positive, the size vector is shifted to the left in a cyclic manner. (The first element is shifted to the last, the second to the first, etc.)
• If k is negative, the size vector is shifted to the right and it packs k leading singleton dimensions to the shifted size vector.

[M, d] = shiftdim(A)

• It removes the leading singleton dimensions of A. d is the number of leading singleton dimensions removed, and M is the array obtained after removing the leading dimensions.

Examples

• Shifting with positive k. The array a has size [1, 2, 3]. Its size vector is shifted towards the left by 1 position in a cyclic manner. Thus, the output has the size [2, 3, 1].

Input

a=randi(10,1,2,3)
b=shiftdim(a,1)
disp('size before shifting')
disp(size(a))
disp('size after shifting')
disp(size(b))

Output

a(:, :, 1) = 
 7.0000   7.0000

a(:, :, 2) = 
 1.0000   5.0000

a(:, :, 3) = 
 5.0000   7.0000

b = 
 7.0000   1.0000   5.0000
 7.0000   5.0000   7.0000

size before shifting
 1.0000   2.0000   3.0000

size after shifting
 2.0000   3.0000   1.0000

• Shifting with negative k. Here k is negative (k == -2) and the dimensions are shifted to the right. It also packs two leading singleton dimensions with ones.

Input

a=randi(10,1,2,3);
% Size before shifting
size(a)
b=shiftdim(a,-2);
% Size after shifting to the right
size(b)

Output

ans =
 1.000   2.000   3.000

ans =
 1.000   1.000   1.000   2.000   3.000

• Remove leading singleton dimensions. The array a has size [1, 1, 2, 3], where the first two dimensions are singleton. Then, shiftdim() removes the singleton dimensions to give M, which has the size [2, 3]. Also d is equal to 2 because two dimensions have been removed.

Input

a = rand(1,1,2,3)
[M,d] = shiftdim(a)

Output

a(:, :, 1, 1) = 1e-1 ×
 3.9131

a(:, :, 2, 1) = 1e-1 ×
 9.5693

a(:, :, 1, 2) = 1e-1 ×
 8.5735

a(:, :, 2, 2) = 1e-1 ×
 6.5399

a(:, :, 1, 3) = 1e-1 ×
 8.9036

a(:, :, 2, 3) = 1e-1 ×
 3.4201

M = 1e-1 × 
 3.9131   8.5735   8.9036
 9.5693   6.5399   3.4201

d = 
 2.0000