How to Group data points and add serial numbers within the group ?

I have a table with ID and Date columns. I want to group the data by ID and add serial numbers in a new column call Serial No. as seen in the example below. How to do this in Matlab ?

Original table:

ID Date

12 jan

12 feb

12 mar

14 jan

14 feb

14 mar

14 apr

11 jan

11 feb

Expected Output:

ID Date Serial No.

12 jan 1

12 feb 2

12 mar 3

14 jan 1

14 feb 2

14 mar 3

14 apr 4

11 jan 1

11 feb 2

Thanks!

Answer 1

[KSSV]

A = [12  1
	 12  2
	 12  3
	 14  1
	 14  2
	 14  3
	 14  4
	 11  1
	 11  2] ;

[c,ia,ib] = unique(A(:,1)) ;
n = length(c) ; 
iwant = zeros(n,2) ; 
for i = 1:n
    iwant(i,1) = c(i) ; 
    iwant(i,2) = sum(A(ib==i,2)) ; 
end
iwant

Answer 2

[Ameer Hamza]

See this example

ID = [1;1;2;2;2];
Date = {'jan', 'feb', 'jan', 'feb', 'mar'}.';

T = table(ID, Date);
T.Serial_no = month(datetime(T.Date, 'InputFormat', 'MMM'));

Result

>> T
T =
  5×3 table
    ID     Date      Serial_no
    __    _______    _________
    1     {'jan'}        1    
    1     {'feb'}        2    
    2     {'jan'}        1    
    2     {'feb'}        2    
    2     {'mar'}        3  

[Namrata Goswami]

The serial number should be on the occurrence of the ID. Not based on the month. I do not have a month column in the actual data.

Thanks!

[Ameer Hamza]

In that case, try this

ID = [1;1;2;2;2];
Date = {'jan', 'feb', 'jan', 'feb', 'mar'}.';

T = table(ID, Date);
T.Serial_no = cell2mat(splitapply(@(x) {(1:numel(x)).'}, T.ID, T.ID));