two columns of numbers with the second one sum on steps according to repeated numbers on first column

Dear experts,

I have an data file with 2 columns, data.txt --> input having thousands of lines...

In the 1st column, an integer number is increasing being repeated several times.

In the output I would like to have the sum of each next value added in the second column for each repeated number on 1st column.

input input output

---------------------

1 0.5 0.5 0.5

1 0.4 0.9 0.5 + 0.4

1 0.2 1.1 0.5 + 0.4 + 0.2

2 0.1 0.1 0.1

2 0.2 0.3 0.1 + 0.2

2 0.4 0.7 0.1 + 0.2 + 0.4

3 0.6 0.6 0.6

3 0.2 0.8 0.6 + 0.2

...................

I did something like:

load data.txt

C=(data(:,2));

[a,b] = unique(data(:,1));

[~,d] = unique(data(:,1),'last');

for i = 1 : size(a,1)

B1(i) = sum(C(b(i):d(i),1));

end

%disp(B1)

B = [B1' a]

But I got

B =

1.1000 1.0000

0.7000 2.0000

0.8000 3.0000

Any help please?

Best regards

Georgios

Answer 1

[Dyuman Joshi]

For continuous repetition -

in1 = [1;1;1;2;2;2;3;3];
in2 = [0.5;0.4;0.2;0.1;0.2;0.4;0.6;0.2];

for k=2:numel(in1)
    if in1(k)==in1(k-1)
        in2(k)=in2(k)+in2(k-1);
    end
end
in2

in2 = 8×1

0.5000 0.9000 1.1000 0.1000 0.3000 0.7000 0.6000 0.8000

[Georgios Tsiledakis]

Thanks so much Joshi!

This is exactly what I would like to proceed.

I am really grateful for your help.

All the best

Georgios