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

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Van Vy
Van Vy 2018-7-7
评论： Van Vy 2018-7-7
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 :)
  2 个评论
Image Analyst
Image Analyst 2018-7-7
I don't know what your edit was, but I did help. My code in my answer below works. Did you try it?

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Image Analyst
Image Analyst 2018-7-7
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.

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