MATLAB: Concatenating more values on a matrix

concatenatingmatrixsort

Hi everyone! I've been struggling with a simple problem for a while but i could not figure it out how to do it. What i want to do is that if it happens to be the same value more then once on the first column is to eliminate the others and add their second column together. For the example in the picture i want:
6 – 0.03;
8 – 0.05;
5 – 0.06;
3 – 0.03;
if true
% v = fix(10*rand(10))
heads = 1:10;
probab = 1:10;
count = 0;
for i = 1:10
heads(i) = v(i);
for j = 1:10
if ( v(i,j) == heads(i) )
count = count + 1;
end
end
probab(i) = count;
count = 0;
end
X = vertcat(heads, probab/100)
end

Best Answer

  • You can do this quite easily using unique and accumarray. In fact solving this kind of problem is exactly what accumarray is intended for:
    >> A = [6,3,8,5,3,9,8,5,6,5;0.01,0.02,0.03,0.01,0.01,0.03,0.02,0.02,0.02,0.03];
    >> [B,~,idx] = unique(A(1,:));
    >> [B.',accumarray(idx(:),A(2,:))]
    ans =
    3 0.03
    5 0.06
    6 0.03
    8 0.05
    9 0.03
    If you have a newer MATLAB version you can use the 'stable' option as well, which might give you the output order you want:
    >> [B,~,idx] = unique(A(1,:),'stable');
    >> [B.',accumarray(idx(:),A(2,:))]
    ans =
    6 0.03
    3 0.03
    8 0.05
    5 0.06
    9 0.03