# MATLAB giving error while trying to create a 3D scatter plot: Error using sparse (Index exceeds array bounds)

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hello_world on 17 Jul 2018
Answered: Walter Roberson on 18 Jul 2018
I was following the MathWorks example: https://www.mathworks.com/help/stats/tsne.html#bvkcm24-1 which works fine for fisheriris dataset.
[Y2,loss2] = tsne(meas,'Algorithm','exact','NumDimensions',3);
figure
v = double(categorical(species));
c = full(sparse(1:numel(v),v,ones(size(v)),numel(v),3));
scatter3(Y2(:,1),Y2(:,2),Y2(:,3),15,c,'filled')
title('3-D Embedding')
view(-50,8)
However, when I change a dataset to something else, it gives error:
Error using sparse
Index exceeds array bounds.
I have the following:
c = full(sparse(1:numel(v), v, ones(size(v)), numel(v), 3));
where numel(v) = 9339, size(v) = 9339 x 1 double
Here the last argument is digit '3' which I followed from MathWorks example in link above. I want to reduce it to 3 dimensions and create a 3D plot same as in that example.
In my case v has 25 classes unlike 3 in Mathworks exaple. So I changed it as follows:
c = full(sparse(1:numel(v), v, ones(size(v)), numel(v), 25));
This time there is no error in c, but I get the error below:
Error using scatter3 (line 109)
C must be a single color, a vector the same length as X, or an M-by-3 matrix.
Walter Roberson on 18 Jul 2018
I would prefer you did not close the question, as it might be of use to other people.
To create a colormap array, just assign to it.
mycmap = [0 0 1;
0 0 .5;
0 0 0;
0 .5 0;
0 .5 .5;
0 .5 1;
0 1 1;
0.5 1 1;
0.5 1 0.5;
0.5 1 0;
0.5 0.5 0;
0.5 0 0 ];
colormap(mycmap)

Walter Roberson on 18 Jul 2018
scatter3(Y2(:,1), Y2(:,2), Y2(:,3), 15, v(:), 'filled');
colormap( jet(numel(unique(v))) )