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

[Jan]

"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?

[akis Lykiardopoulos]

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

Answer 1

[Shunichi Kusano]

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.

[akis Lykiardopoulos]

thanks a lot for the help !!!

Answer 2

[Jan]

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

[akis Lykiardopoulos]

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