MATLAB中的数组内部数组

Question

If n=4 for example, How to create an array like this in MATLAB?

[[0] [0 0] [0 0 0] [0 0 0 0]]

Is there a way to create an array inside a for loop, for example ? This is what I want to achieve (I know it's wrong code):

for i=1:n
   table(i)=zeros(i);
end

Answer 1

You need a cell array to hold your numeric vectors. Cell arrays are used in Matlab when the contents of each cell are of different size or type.

Additional comments:

• I'm renaming your variable i to k , to avoid shadowing the imaginary unit.
• I'm also renaming your variable table to t , to avoid shadowing the table function.
• zeros(k) gives a k x k matrix of zeros. To obtain a row vector of zeros use zeros(1,k) .
• It's better to preallocate the cell array to improve speed.

Taking the above into account, the code is:

n = 4;
t = cell(1,n); %// preallocate: 1xn cell array of empty cells
for k = 1:n
   t{k} = zeros(1,k);
end

This gives:

>> celldisp(t)
t{1} =
     0
t{2} =
     0     0
t{3} =
     0     0     0
t{4} =
     0     0     0     0

Equivalently, you could replace the for loop by the more compact arrayfun :

result = arrayfun(@(k) zeros(1,k), 1:n, 'uniformoutput', false);