I want to sum up specific array in a matrix

For example If I have a matrix like this

x = [ 2.356 37

1.351 39

4.394 37

3.622 39

4.489 39

3.135 37

6.653 39 ]

I want to sum up the values that are specific to 37 and 39 seperatly only if it is alternative. If 39 and 37 are not alternative like in 4th and 5 th row wants to add that to the next subsecuent value in this case it is 37.

Some of the 37 should be (2.356+4.394+4.489+3.135), 39 should be (1.351+3.622+6.653). Please help in getting a matlab code for this!

Thank you in advance

[Andrei Bobrov]

x = [   2.356           37
        1.351           39
        4.394           37
        3.622           39
        4.489           39
        3.135           37
       3.5147           37
       3.6058           37
        2.827           37
       3.6134           37
        6.653           39];

result - ??

[Bhagya Lakshmi Marella]

sum_37 should be =2.356+4.394+4.489+3.135

sum_39 should be =1.351+3.622+3.5147+3.6058+2.827+3.6134+6.653

[Bhagya Lakshmi Marella]

sum_37 should be =2.356+4.394+4.489+3.135

sum_39 should be =1.351+3.622+3.5147+3.6058+2.827+3.6134+6.653

Please help me to get this!

Answer 1

[Shwetank Shrey]

Hope this helps you.

function [sum_37, sum_39] = compute_sum(x)
    sum_37 = 0;
    sum_39 = 0;
    found_37 = false;
    found_39 = false;
    for i = 1 : length(x)
        if x(i, 2) == 37
            if ~found_37 
                sum_37 =  sum_37 + x(i, 1);
                found_37 = true;
                found_39 = false;
            else
                sum_39 =  sum_39 + x(i, 1);
            end
            else
            if ~found_39 
                sum_39 =  sum_39 + x(i, 1);
                found_39 = true;
                found_37 = false;
            else
                sum_37 =  sum_37 + x(i, 1);
            end
        end
    end
end

[Bhagya Lakshmi Marella]

Thank you so much it works.

Answer 2

[KALYAN ACHARJYA]

x =[2.356 37 
  1.351 39 
  4.394 37 
  3.622 39 
  4.489 39 
  3.135 37 
  6.653 39]
idx=(find(x(:,2)==37))';
sum_37=0;
for i=1:length(idx)
sum_37=sum_37+x(idx(i),1);
end 
% You can do the same for 39 too

Wait I am providing the same without loop

idx=(find(x(:,2)==37))';
sum_37=sum(x(idx(:),1));

For 39:

idx=(find(x(:,2)==39))';
sum_39=sum(x(idx(:),1));

[Bhagya Lakshmi Marella]

Thank you so much!

This works to add up the elements that are specific to a 37 and 39. But, If 39 and 37 are not alternative like in 4th and 5 th row, I want to add that to the next subsecuent value in this case 4.489 should be added to 37.

[KALYAN ACHARJYA]

You can do that using 1/2 line of logical statments and index comparision.