Produce a new matrix,Z from X and Y matrices

I have 2 matrices, and I would like to derive another matrix, Z from X and Y. So for each row starting and ending the same, sum of their corresponding values in X. For example, in Y, any row starting and ending with 1 and 2 respectively, loop up at their X values, and sum them up i.e. 25+1+3=29. Then perform the same method for the rest.

X = [25;

1;

3;

28;

6;

7;

25;

6;

9;

25;

10;

11;

15;

14;

12;

13;

25;

14;

15;]

Y = [1 2 0 0;

1 3 2 0;

1 4 3 2;

1 3 0 0;

1 2 3 0;

1 4 3 0;

1 4 0 0;

1 3 4 0;

1 2 3 4;

2 3 0 0;

2 1 3 0;

2 1 4 3;

2 1 4 0;

2 3 4 0;

2 1 3 4;

2 3 1 4;

3 4 0 0;

3 1 4 0;

3 2 1 4;]

Z = [25+1+3; % start ‘1’ and end with ‘2’

28+6+7; % start ‘1’ and end with ‘3’

25+6+9; % start ‘1’ and end with ‘4’

25+10+11; % start ‘2’ and end with ‘3’

15+14+12+13; % start ‘2’ and end with ‘4’

25+14+15;] % start ‘3’ and end with ‘4’

Answer 1

[Star Strider]

One option:

for k = 1:size(Y,1)
    [~,Zc] = find(Y(k,:) ~= 0, 1, 'last');              % Last Non-Zero Column
    Z2(k,:) = Y(k,Zc);                                  % Element Of Last Non-Zero Column
end

Z = accumarray([Z2 Y(:,1)], X)

producing:

Z =
     0     0     0
    29     0     0
    41    46     0
    40    54    54

To print it out:

[Zs,Ze] = meshgrid(1:3, 1:4);
Zsc = Zs(:);
Zec = Ze(:);
fprintf(1, 'Starts with %d, Ends with %d, Z = %2d\n', [Zs(:), Ze(:), Z(:)]')

producing:

Starts with 1, Ends with 1, Z =  0
Starts with 1, Ends with 2, Z = 29
Starts with 1, Ends with 3, Z = 41
Starts with 1, Ends with 4, Z = 40
Starts with 2, Ends with 1, Z =  0
Starts with 2, Ends with 2, Z =  0
Starts with 2, Ends with 3, Z = 46
Starts with 2, Ends with 4, Z = 54
Starts with 3, Ends with 1, Z =  0
Starts with 3, Ends with 2, Z =  0
Starts with 3, Ends with 3, Z =  0
Starts with 3, Ends with 4, Z = 54

Experiment to get the result you want.

[JL]

Thank you very much for your assistance on this query. Do you think its possible to get the values as

Z = [ 0 29 41 40

29 0 46 54

41 46 0 54

40 54 54 0]

[Star Strider]

As always, my pleasure.

One way:

Z1 = [Z, zeros(size(Z,1),1)];
Z2 = [Z.'; zeros(1,size(Z,1))];
Znew = Z1 + Z2

producing:

Znew =
     0    29    41    40
    29     0    46    54
    41    46     0    54
    40    54    54     0
    

This creates equal-dimension matrices by augmenting the original and its transpose with a column of zeros and a row of zeros respectively, then adding the resulting matrices.

[JL]

Thank you very much! :)

[Star Strider]

As always, my pleasure!

This was an interesting problem!

[JL]

Star Strider, I have another intetesting problem, was wondering if you are interested to take a look - here is the link to the question https://uk.mathworks.com/matlabcentral/answers/475460-sharing-values-of-elements-in-a-matrix