MATLAB: New column in matrix based on condition from other matrix

new column in matrix based on condition from other matrix

I have a matrix a = [ 1 11; 2 11; 3 12; 4 12; 5 13; 6 13] and b = [1;1;2;3;4;3;5;5;2;3] I want a new column in b based on the second column from a matrix i.e the output should be b = [1 11; 1 11; 2 11; 3 12; 4 12; 3 12; 5 13; 5 13; 2 11; 3 12]. Please can anyone help as soon as possible. it is very urgent!! Waiting for answers, Thanks in advance.

Best Answer

[found, arow] = ismember(b, a(:, 1));
assert(all(found), 'some elements of b are not in a');
b(:, 2) = a(arow, 2);

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MATLAB: How to sepeperate a set of data to a new matrix from two set of matrix

Here is a generic way of splitting the original matrix into submatrices according to your condition:

function C = splitmatrix(A, B, indexcol)
   %indexcol: a scalar integer >=1
   %A: a M x N matrix, with N >= indexcol. the elements of A(:, indexcol)) must be unique
   %B: a P x 2 matrix. Column 1 of B must match one value of A(:, indexcol). Column 2 of B must be integer >= 1
   %C: cell array output of size max(B(:, 2) x 1. 
   %C{k} is a matrix whose rows are the rows of A for which A(:, indexrow) is found in B(1, B(:, 2) == k)
   %validate above preconditions
   validateattributes(indexcol, {'numeric'}, {'scalar', 'integer', 'positive'});
   validateattributes(A, {'numeric'}, {'2d'});
   assert(size(A, 2) >= indexcol, 'indexcol is greater than the number of columns of A');
   assert(numel(unique(A(:, indexcol))) == size(A, 1), 'some elements of A(:, indexcol) are non unique');
   validateattributes(B, {'numeric'}, {'2d', 'ncols', 2});
   assert(all(ismember(A(:, indexcol), B(:, 1))), 'some elements of B(:, 1) are not found in A:, indexcol)');
   validateattributes(B(:, 2), {'numeric'}, {'integer', 'positive'}, '', 'second column of B');
   %find the rows of A that match first column of B:
   Arows = arrayfun(@(indexval) find(A(:, indexcol) == indexval), B(:, 1));
   %concatenate Arows according to the index in B(:, 2):
   rowsdestination = accumarray(B(:, 2), Arows, [], @(v) {v});
   %split A according to the destination:
   C = cellfun(@(rows) A(rows, :), rowsdestination, 'UniformOutput', false);
end

MATLAB: Reshape 3d matrix to obtain a column vector

A(:,:,1) = [1 2 3; 4 5 6; 7 8 9]
A(:,:,2) = [10 11 12; 13 14 15; 16 17 18]
A(:,:,3) = [19 20 21; 22 23 24; 25 26 27]
B=permute(A,[2 1 3])
out=B(:)

Best Answer

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MATLAB: How to sepeperate a set of data to a new matrix from two set of matrix

MATLAB: Reshape 3d matrix to obtain a column vector

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