How to assing incrementing numbers to identical values in a column?

Hello to all,

my ultimate goal of this question is to find a solution for the following problem: I am searching for the index of the first and last day of a month of one year specifically. To specify my question here a design of my data :

Column 1(Year) Column 2(Month) Column 3(Data)

1990 1 .098

1990 1 .99

1990 1 .34

1990 2 .56

1990 2 .44

In this example my answer would be IndexBeginning = 1 and IndexEnding= 3 for month 1 of the year 1990 and IndexBeginning = 4 and IndexEnding= 5 for month 2 of the year 1990.

To get specific values for a month and the respective years i have already merged the two first columns. January 1990, e.g., now has the designated number 19901 and February 1995 the number 19952. Now I´m trying to index those merged numbers from 1 to 293 ( number of month of my sample) in correct order so i can easily search for every month.

I´m very grateful for any and every idea!

with Kind Regards,

A Goeh

Answer 1

[Azzi Abdelmalek]

M=[1990 1 .098;1990 1 .99;1990 1 .34;1990 2 .56;1990 2 .44]
[ii,jj,kk]=unique(M(:,1:2),'rows','stable')
out=[ii cell2mat(accumarray(kk,(1:numel(kk))',[],@(x) {[x(1) x(end)]}))]

[A. Goeh]

Thank you very much!! It works perfectly and I wouldn´t have thought of such an elegant way of solving this problem.

Answer 2

[Andrei Bobrov]

M = [1990 1 .098;1990 1 .99;1990 1 .34;1990 2 .56;1990 2 .44];

[ii,jj] = unique(M(:,1:2),'rows','first');
[~,kk]  = unique(M(:,1:2),'rows','last');
out = [ii,jj,kk];