How to combine random size arrays in one matrix - in a loop?

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Jeroen
Jeroen el 15 de En. de 2014
Editada: Venkat Ta el 3 de Mayo de 2018
Hey, I've been able to find a lot of solutions for my matlab program on this site but the next problem still goes unanswered.
I have a loop in which every run a vector is created with a random size. After the loop is finished I want all these vectors presented in a matrix with each vector as a column. How can I do this? The shorter vectors may either be filled with NaN's or zero's.
In essence the program looks like this:
for i=1:1:10;
l=ceil(rand(1)*10);
vector=rand(l,1);
end
matrix=[vector1 vector2 ... vector10 ];
Thanks in advance for helping me out.

Respuesta aceptada

Mischa Kim
Mischa Kim el 15 de En. de 2014
Editada: Mischa Kim el 15 de En. de 2014
Hello Jeroen,
  • Generate the vectors - I'll call them b - in your for-loop and keep track of the longest vector that is generated in the loop. Store the vectors as a matrix: b(:,ii).
  • Once done, initialize a 0-matrix A using zeros(M,N) where M is equal to the size of the longest vector and N is the total number of vectors.
  • Lastly run another for-loop to paste into the matrix the individual vectors using something like:
A(:,ii) = [b(:,ii); zeros(length(A(1,:)) - length(b(:,ii)),1)]
where ii is the running index of the loop.
You can also get this done using only one loop, of course, by simply concatenating vectors that have been "filled up" with the adequate number of 0s, or filling up the existing matrix before concatenating.
  2 comentarios
Mischa Kim
Mischa Kim el 16 de En. de 2014
Run the code below. Not optimized but it does what you are looking for:
A = [0];
for ii = 1:10
b = ones(randi([1,10],1,1), 1); % here you put your random-sized vector
if (size(A(:,1)) == 1)
A = b;
else
if (length(b) < length(A(:,1)))
A = [A [b; zeros(length(A(:,1)) - length(b),1)]];
end
if (length(b) == length(A(:,1)))
A = [A b];
end
if (length(b) > length(A(:,1)))
A = [[A; zeros(length(b) - length(A(:,1)), length(A(1,:)))] b];
end
end
end
display(A);
Venkat Ta
Venkat Ta el 3 de Mayo de 2018
it works in between the program but this whole code does not work if I created as function

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Más respuestas (3)

Jos (10584)
Jos (10584) el 16 de En. de 2014
Editada: Jos (10584) el 16 de En. de 2014
You have several options how to store vectors with different lengths.
1) use cell arrays
C = cell(k,1) ;
for k=1:10,
L = ceil(10*rand) ;
C{k} = rand(L,1) ;
end
2) subsequently you can concatenate these cells into a single array, in which shorter vectors are padded with a chosen value. I have submitted the function PADCAT to the file exchange, which makes this a trivial conversion:
[M, tf] = padcat(C{:}) % pad with NaNs by default
M(~tf) = 0 % change NaNs to zeros

Amit
Amit el 16 de En. de 2014
how about:
matrix = zeros(10,10);
flag = 1;
for i = 1:10
m = randi(10);
matrix(1:m,flag:flag+m-1) = rand(m);
flag = flag + m;
end

Andrei Bobrov
Andrei Bobrov el 16 de En. de 2014
for jj = 1:10
v = randi(randi(234),randi(12),1);
if jj==1
out = v;
else
n = [size(out,1),numel(v)];
out(n(1)+1:n(2),1:jj-1) = nan;
out(1:max(n),jj) = nan;
out(1:n(2),jj) = v;
end
end
  2 comentarios
Charles
Charles el 4 de Ag. de 2017
All great answers The simpler the better!!
Venkat Ta
Venkat Ta el 26 de Abr. de 2018
Editada: Venkat Ta el 3 de Mayo de 2018
Thanks. It works fine.
it works in between the program but this whole code does not work if I created as function

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