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a 2D into a 3D Array

Hello people,
I have a a 2D array (is the spectogram of a song with only the real values) and i want to convert it to a 3D. How i will do it? I will take my X Y array (34801 2049) and i will make a new 3D with (9, 2049, 3867) simply by cutting my big array every 9 lines and put them into the 3D in the first frame then for the next i will cut from 10 to 18 the big 2D array and so on.
i wrote this:
begin=1;
end=9;
for i=1:3866
a(:,:,T)=PICT(begin:end,:);
begin=begin+9;
end=end+9;
end
where a is my 3D array and PICT is my 2D array
It does not work for some reason... is there any way in matlab to do it without doing 3 loops?
Hope i was clear
thx in advance for your reply

  2 Comments

Jan
on 11 Jun 2019
"end" is an important Matlab command. You cannot re-use the name as a variable. You should see a corresponding error message.
The loop counter is "i", but you use "T" inside the loop. Is this a typo?
you are right about this. My apologies. I wrote variables with different names in matlab and here i change their name in order to be more understandable (bad idea).
thx for the reply

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2 Answers

Answer by Shunichi Kusano on 11 Jun 2019
 Accepted Answer

Hi. You can do it by reshape and permute like:
PICT = [PICT; zeros(2, 2049)]; % (34803 2049)
a = reshape(PICT.', 2049, 9, 3867); % (2049, 9, 3867)
a = permute(a, [2 1 3]); % (9, 2049, 3867)
hope this helps.

  1 Comment

thanks a lot for the help !!!

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Jan
Answer by Jan
on 11 Jun 2019
Edited by Jan
on 11 Jun 2019

Prefer Shunichi Kusano's solution. But for completeness:
ini = 1;
fin = 9;
a = zeros(9, 2049, 3867);
m = size(PICT, 1);
for k = 1:3867
a(1:fin - ini + 1, :, k) = PICT(ini:fin, :);
ini = min(ini + 9, m);
fin = min(fin + 9, m);
end

  1 Comment

thx for your time. It helped me understand my mistakes.

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