what is meant by singleton dimension?

what is meant by singleton dimension?

Answer 1

[Image Analyst]

That's a dimension that has a length of 1. For example, if you had a 3D image that is 400 rows by 1 column by 200 slices, the second dimension (columns) would be a singleton since it's one. You'd have only one image plane running in the y-z direction (rows-slices). You can get back to a 2D image by using squeeze() to remove the singleton dimension.

[Minions]

is there any example of this?

[Image Analyst]

Try this:

% Create a 3-D matrix with 2 rows, 4 columns, and 3 slices:
M3d = randi(9, 2, 4, 3)

% Extract slice 2.  No singleton dimension since we're extracting the last index.
slice2 = M3d(:, :, 2) % Size is 2x4
whos slice2

% Extract slice that is essentially pulling the matrix
% that represents column 2 from the rectangular block.
% There will be a singleton dimension since we're NOT extracting the last index.
slice3 = M3d(:, 2, :) % Size is 2x1x3
whos slice3

% Run squeeze on slice 3 to get a 2x3 matrix, which is what you really wanted.
slice3a = squeeze(slice3)
whos slice3a

You get:

M3d(:,:,1) =

2 4 6 9

1 7 5 1

M3d(:,:,2) =

5 5 6 4

2 6 2 3

M3d(:,:,3) =

6 7 6 4

6 2 7 4

slice2 =

5 5 6 4

2 6 2 3

Name Size Bytes Class Attributes

slice2 2x4 64 double

slice3(:,:,1) =

4

7

slice3(:,:,2) =

5

6

slice3(:,:,3) =

7

2

Name Size Bytes Class Attributes

slice3 2x1x3 48 double

slice3a =

4 5 7

7 6 2

Name Size Bytes Class Attributes

slice3a 2x3 48 double

[Swati Sarangi]

@Image Analyst

I've a doubt here, M3d = randi(9, 2, 4, 3)

What does '9' indicate in the above command?

[Image Analyst]

That is the max value that the random numbers in the 2-by-4-by-3 three-D matrix can take on. Did you look up randi in the help documentation? It describes it there.