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Why is MATLAB not hiding 2D trailing singleton dimension?

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3

A MATLAB array has an infinite number of trailing singleton dimension (theoretically).

So a 1x10 array is in fact a 1x10x1x1x1... array. I suppose that MATLAB just hides the trailing singleton dimension.

You can observe this behaviour with this code snippet:

permute([1:10],[2,1,4,3])

MATLAB deals with permuting the 3rd and 4th dimension without any problem even if it's a 1D array.

But why does MATLAB not hide the trailing singleton dimension in the 2nd dimension?

---

size(rand(10,1))

gives:

ans =

 10 1

---

size(rand(10,1,1))

also gives:

ans =

 10 1

Is that because MATLAB is optimized for linear algebra? So, is it simply a convention?

arrays matlab multidimensional-array

share|improve this question

edited Mar 25 at 18:58

Sardar Usama

16.3k88 gold badges2727 silver badges4949 bronze badges

asked Mar 25 at 17:07

obchardonobchardon

4,72611 gold badge88 silver badges2222 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  By definition, MATLAB arrays always have at least two dimensions. This is by design. Originally, everything was 2D. At some point they introduced higher-dimensional arrays (I think this was MATLAB 5, but am not sure). But I guess they couldn't remove the last singleton dimension to allow 1D arrays because it would break a lot of code.
  
  – Cris Luengo
  Mar 25 at 17:11
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ho you're right, I've just found this explaination: "Arrays in MATLAB are N-dimensional, with an infinite number of trailing singleton dimensions. Trailing singleton dimensions past the second are not displayed or reported on, e.g., with size. No array has fewer than two dimensions. Empty arrays are the logical extension of general arrays but have at least one size 0 dimension. The syntax [] denotes the empty array of size 0x0 and is treated as an exception occasionally (for backward compatibility)"
  
  – obchardon
  Mar 25 at 17:19
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That quote should read "Arrays in MATLAB are N-dimensional, with N ∈ [2,∞)." :)
  
  – Cris Luengo
  Mar 25 at 17:23
  
  

  
  
  
  

add a comment | 

3

A MATLAB array has an infinite number of trailing singleton dimension (theoretically).

So a 1x10 array is in fact a 1x10x1x1x1... array. I suppose that MATLAB just hides the trailing singleton dimension.

You can observe this behaviour with this code snippet:

permute([1:10],[2,1,4,3])

MATLAB deals with permuting the 3rd and 4th dimension without any problem even if it's a 1D array.

But why does MATLAB not hide the trailing singleton dimension in the 2nd dimension?

---

size(rand(10,1))

gives:

ans =

 10 1

---

size(rand(10,1,1))

also gives:

ans =

 10 1

Is that because MATLAB is optimized for linear algebra? So, is it simply a convention?

arrays matlab multidimensional-array

share|improve this question

edited Mar 25 at 18:58

Sardar Usama

16.3k88 gold badges2727 silver badges4949 bronze badges

asked Mar 25 at 17:07

obchardonobchardon

4,72611 gold badge88 silver badges2222 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  By definition, MATLAB arrays always have at least two dimensions. This is by design. Originally, everything was 2D. At some point they introduced higher-dimensional arrays (I think this was MATLAB 5, but am not sure). But I guess they couldn't remove the last singleton dimension to allow 1D arrays because it would break a lot of code.
  
  – Cris Luengo
  Mar 25 at 17:11
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ho you're right, I've just found this explaination: "Arrays in MATLAB are N-dimensional, with an infinite number of trailing singleton dimensions. Trailing singleton dimensions past the second are not displayed or reported on, e.g., with size. No array has fewer than two dimensions. Empty arrays are the logical extension of general arrays but have at least one size 0 dimension. The syntax [] denotes the empty array of size 0x0 and is treated as an exception occasionally (for backward compatibility)"
  
  – obchardon
  Mar 25 at 17:19
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That quote should read "Arrays in MATLAB are N-dimensional, with N ∈ [2,∞)." :)
  
  – Cris Luengo
  Mar 25 at 17:23
  
  

  
  
  
  

add a comment | 

A MATLAB array has an infinite number of trailing singleton dimension (theoretically).

So a 1x10 array is in fact a 1x10x1x1x1... array. I suppose that MATLAB just hides the trailing singleton dimension.

You can observe this behaviour with this code snippet:

permute([1:10],[2,1,4,3])

MATLAB deals with permuting the 3rd and 4th dimension without any problem even if it's a 1D array.

But why does MATLAB not hide the trailing singleton dimension in the 2nd dimension?

---

size(rand(10,1))

gives:

ans =

 10 1

---

size(rand(10,1,1))

also gives:

ans =

 10 1

Is that because MATLAB is optimized for linear algebra? So, is it simply a convention?

arrays matlab multidimensional-array

share|improve this question

edited Mar 25 at 18:58

Sardar Usama

16.3k88 gold badges2727 silver badges4949 bronze badges

asked Mar 25 at 17:07

obchardonobchardon

4,72611 gold badge88 silver badges2222 bronze badges

permute([1:10],[2,1,4,3])

size(rand(10,1))

ans =

 10 1

size(rand(10,1,1))

ans =

 10 1

share|improve this question

edited Mar 25 at 18:58

Sardar Usama

16.3k88 gold badges2727 silver badges4949 bronze badges

asked Mar 25 at 17:07

obchardonobchardon

4,72611 gold badge88 silver badges2222 bronze badges

share|improve this question

edited Mar 25 at 18:58

Sardar Usama

16.3k88 gold badges2727 silver badges4949 bronze badges

asked Mar 25 at 17:07

obchardonobchardon

4,72611 gold badge88 silver badges2222 bronze badges

edited Mar 25 at 18:58

Sardar Usama

16.3k88 gold badges2727 silver badges4949 bronze badges

edited Mar 25 at 18:58

Sardar Usama

16.3k88 gold badges2727 silver badges4949 bronze badges

asked Mar 25 at 17:07

obchardonobchardon

4,72611 gold badge88 silver badges2222 bronze badges

asked Mar 25 at 17:07

obchardonobchardon

4,72611 gold badge88 silver badges2222 bronze badges