How to extract a field from a structure?

I want to extract an entire field from structures with multiple fields and store it in a vector:

vector = S.(sample)

only returns me row 1

vector = S(2).data

This would return me the second position but when I try to extract all the data

vector = S.data

or

vector = S(:).data

I still get only 24x250x50 double, and not all the data column.

Thank you!

[Stephen23]

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them

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

Answer 1

[Voss]

% making a struct array with two fields:
S = struct('sample',num2cell(1:10),'info',sprintfc('information_%d',1:10))

S = 1×10 struct array with fields:
    sample
    info

% get the 'sample' field from each element of S, put them in a vector:
vector = [S.sample]

vector = 1×10

1 2 3 4 5 6 7 8 9 10

% get the 'info' field from each element of S, put them in a cell array:
cell_array = {S.info}

cell_array = 1×10 cell array
    {'information_1'}    {'information_2'}    {'information_3'}    {'information_4'}    {'information_5'}    {'information_6'}    {'information_7'}    {'information_8'}    {'information_9'}    {'information_10'}

More information: https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists#answer_250868

[RST]

That is the first time I have come across the undocumented built-in function 'sprintfc'.

[Voss]

@RST: FYI, compose is the documented built-in function that operates similarly to sprintfc.

compose('information_%d',1:3)

ans = 1×3 cell array
    {'information_1'}    {'information_2'}    {'information_3'}

It's also worth pointing out that string concatenation is convenient in some contexts.

"information_" + (1:3)

ans = 1×3 string array
    "information_1"    "information_2"    "information_3"

[RST]

Many thanks for that! Your comment inspired my answer in

https://uk.mathworks.com/matlabcentral/answers/21-how-do-i-convert-a-numerical-vector-into-a-comma-delimited-string