sum of consecutive months value in an array

Hello: I have an array where the first, second and third columns show year, month and values. I need to sum the values of consecutive months. The matrix X is as below

1988  6  223.12
1994  7  1033.0
1994  8  464.67
1995  9  251.33
1997  6  121.41
1997  8  624.58
1999  9  221.60
2001  7  782.04

The desired output:

1988  223.12
1994  1497.67
1995  251.33
1997  121.41
1997  624.58
1999  221.60
2001  782.04

I have tried like this:

dt = datetime([X(:,1:2), repmat([0 0 0 0],length(X),1)]);

Monthgroup = cumsum([1; months(diff(datetime([X(:,1:2), repmat([0 0 0 0],length(X),1)]))) == 1]);

where same year with a different month, example, 1994 in this case, will suppose to show a common index but I am getting some error. Based on this common index, could I use accumarray function? Any help will be appreciated. Thanks,

[jonas]

I guess it needs to work for any number of consecutive months?

[Poulomi Ganguli]

yes but for the same year not for different years.

Answer 1

[Andrei Bobrov]

a = [1988  6  223.12
1994  7  1033.0
1994  8  464.67
1995  9  251.33
1997  6  121.41
1997  8  624.58
1999  9  221.60
2001  7  782.04 ];

b = datetime(a(:,1),a(:,2),1);
lo = [true; b(1:end-1) + calmonths(1) ~= b(2:end)];
out = [a(lo,1), accumarray(cumsum(lo),a(:,3))];

or

b2 = a(:,1:2)*[12;1];
lo2 = [true;diff(b2) ~= 1];
out2 = [a(lo2,1), accumarray(cumsum(lo2),a(:,3))];

[Poulomi Ganguli]

The code works nicely. To be curious, What is the function of this line?

lo = [true; b(1:end-1) + calmonths(1) ~= b(2:end)];

Could you please explain?

[Rik]

Unfortunately, this merges 1996-12 and 1997-1, which was not the intention if I understood you correctly. A slight edit of the second method seems to fix this:

b2 = a(:,1:2)*[13;1];
lo2 = [true;diff(b2) ~= 1];
out2 = [a(lo2,1), accumarray(cumsum(lo2),a(:,3))]

[Poulomi Ganguli]

Thanks, but I want to merge 1996-12 and 1997-1 since this gives me a continuous series. For other months this won't be applicable. Hence, I think I should go for the 1st method, is isn't it?

[Andrei Bobrov]

lo - a logical vector where each value determines that the difference between specific value of b-vector and the previous value of the b-vector is not equal of one month.

And please read about functions of MATLAB datetime and calmonths.

use:

>> datetime([2018;2019],[7;12],1) + calmonths(1)
ans = 
  2×1 datetime array
   01-Aug-2018
   01-Jan-2020
>>

[Rik]

If you want to merge them, use either of the methods Andrei posted, if not, use the adapted code I posted in my comment. Which is the correct version for you depends on your application.

[Poulomi Ganguli]

Thanks! Now it's clear.