how can I reshape vector data into a matrix

Can anyone help me with this please... I have a data set, shaped so. This needs to be graphed in 3D.

The first column represents locations on X-axis, the 2nd column - locations on Y-axis, and the third column is my data. The 1st & 2nd column make a grid.

How do I reshape this to make the 3rd column into a 2x2 matrix, so that the whole thing can be graphed as a surface?

Thank you beforehand!

D.

Answer 1

[Guillaume]

How do I reshape this to make the 3rd column into a 2x2 matrix, so that the whole thing can be graphed as a surface?

You don't, it's completely unnecessary

surf(yourmatrix(:, 1), yourmatrix(:, 2), yourmatrix(:, 3));

If you wanted to do the reshape (which again is completely unnecessary), and assuming that the X and Y coordinates that are supposed to be identical are actually identical down to the last binary digit, then:

[~, ~, col] = unique(yourmatrix(:, 1));
[~, ~, row] = unique(yourmatrix(:, 2));
X(row, col) = yourmatrix(:, 1);
Y(row, col) = yourmatrix(:, 2);
Z(row, col) = yourmatrix(:, 3);

[Daria Bontch-Osmolovskaia]

Guillaume, thank you. I've tried using the SURF function, and I get an error message "Z must be a matrix, not a scalar or vector." Which is why I'm asking about reshaping...

[Rik]

It feels like it should be a valid input, but it isn't. That is one of my frustrations with surf as a function.

[Guillaume]

Doh! Indeed Z has to be a matrix. And the second part of the answer was also incorrect. Never mind, this is correct:

[X, ~, col] = unique(yourmatrix(:, 1));
[Y, ~, row] = unique(yourmatrix(:, 2));
Z = zeros(numel(Y), numel(X));
Z(sub2ind(size(Z), row, col)) = yourmatrix(:, 3));

[Daria Bontch-Osmolovskaia]

Guillame, thank you very much - that worked beautifully. Quite literally. Looks like the aurora :) Really appreciate your effort. Prior to this, I was only able to graph data interpolated, and that didn't work right. This is much better as I can see the crazy outliers. Cheers, Daria