How to change the matrix size and value in matlab code?

Hi everyone,

I'm a newbie in matlab. I have a question and hope to receive your surpport.

I have a matrix 3 columns, n rows, like this:

(column 1 and 2 are integer, column 3 is real number)

1  - 2  - a12,
1  - 3  - a13,
2  - 1  - a21,
2  - 3  - a23,
3  - 3  - a33,
4  - 1  - a41,
4  - 2  - a42,

Now I want to change the matrix above become this matrix: (means that the value of column 1 and column 2 about will become the index of new matrix, if don't have index in some position, the new matrix value at that position will be blank)

NaN -  a12 - a13,
a21 -  NaN - a23,
NaN -  NaN - a33,
a41 -  a42 - NaN,

Have anyone help me? I'm looking forward your respond so much :)

[Image Analyst]

I don't know what your edit was, but I did help. My code in my answer below works. Did you try it?

[Van Vy]

Oh, Thank you so so much, that's all I need :) <3

Answer 1

[Image Analyst]

This will do it:

% Sample data.
m1 = [...
1 ,  2  , 100,
1 ,  3 ,  101,
2 ,  1  , 102,
2  , 3  , 103,
3 ,  3 ,  104,
4 ,  1  , 106]

[rows, columns] = size(m1)
% Figure out how many rows and columns we'll need in the output array.
uniqueRows = unique(m1(:, 1))
uniqueCols = unique(m1(:, 2))
% First create an array of all nans.
output = nan(max(uniqueRows), max(uniqueCols))
% Now go through the input array placing the values
% into the output array at the correct location.
for row = 1 : rows
  thisRow = m1(row, 1);
  thisCol = m1(row, 2);
  output(thisRow, thisCol) = m1(row, 3);
end
output % Print to command window.

[Van Vy]

It's so helpful <3 Thank you :)