Vertical concatenation of structure fields (compact form)

Hi,

I know there is a similar question but it's not about the compact form.

My question is: why does the following not result in a vertical concatenation? (it also fails for numerical values)

Or, how can I change it to concatenate vertically into ['value_1' ; 'value_2'] ?

Thanks!

>> structure(1, 1).field = 'value_1';
>> structure(2, 1).field = 'value_2';
>> [structure(:, 1).field]

ans =

    'value_1value_2'

>> 

Answer 1

[Stephen23]

Your example concatenates horizontally because it is exactly equivalent to doing this:

[structure(1).field,structure(2).field]

which is just shorthand for

horzcat(structure(1).field,structure(2).field)

If you want to concatenate vertically, use either of these

vertcat(structure.field)
cat(1,structure.field)

For more information on how to use comma-separated lists:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

[Massimiliano Zanoli]

Thank you for this answer. cat(d, {:}) seems to be the way.

It's interesting that this turns into a vertical array:

>> array = [1 ; 2 ; 3 ; 4];
>> array(:, 1)

ans =

     1
     2
     3
     4

but this turns into a horizontal one:

>> structure(1, 1).field = 1;
>> structure(2, 1).field = 2;
>> structure(3, 1).field = 3;
>> structure(4, 1).field = 4;
>> [structure(:, 1).field]

ans =

     1     2     3     4

Feels a bit inconsistent to me.

[Stephen23]

Comma-separated arrays are equivalent to values separated by commas, not by semi-colons. So this:

structure.field

is equivalent to

structure(1).field,structure(2).field, .. ,structure(end).field

by the very definition of comma-separated lists. There is no equivalent syntax for semi-colon-separated lists.

[Massimiliano Zanoli]

I agree, but (:, 1) should indicate vertical arrangement. That [] defaults to horzcat is a choice, not a must.

Answer 2

[Bjorn Gustavsson]

This gets you to a 2-by-suitable char array:

char(structure.field)

But this will obviously not be a general solution for fields of different data-types.

HTH

Answer 3

[Ameer Hamza]

By default [] is equivalent to horizontal concatination hozcat(). Use vertcat() for vertical output

vertcat(structure.field)