Finding rows of minimum valueS by group

I want to select the rows with the lowest values (more than one) by group

In the following for each date3( col:2), I want to select the rowS with the lowest TimeToMaturity(6)

Answer 1

[KSSV]

Let date2 and TimeToMaturity be your two column arrays.

[c,ia,ib] = unique(date2) ;
N = length(c) ;
iwant = zeros(N,1) ;
for i = 1:N
    iwant(i) = min(TimeToMaturity(ib==i)) ; 
end
[c iwant]

[Afak Nazim]

Thank you for your reply. However it does not solve the problem. It doesnt select the rows, it just gives an array of minimum values

[KSSV]

 iwant(i) = min(TimeToMaturity(ib==i)) ; 

The above line gives index, if you modify it to:

  [iwant(i),idx] = min(TimeToMaturity(ib==i)) ; 

You have the index in hand...you can pick it. REad the documentation of min

[Afak Nazim]

idx is an integer with a value of 1. Not sure this qualifies as an index..

[KSSV]

Index should be a integer...it shall qualify...

Answer 2

[Voss]

Some data like your date3 and TimeToMaturity columns (just using 1, 2, 3, 4 for date here):

date = reshape(repmat(1:4,5,1),[],1);
time_to_maturity = randi(100,20,1);
disp([date time_to_maturity]);

     1    86
     1    64
     1    44
     1    18
     1    60
     2    37
     2    72
     2    98
     2    60
     2     3
     3    62
     3    22
     3    22
     3    82
     3    67
     4    49
     4    70
     4    39
     4    73
     4    62

Now find the minimum time_to_maturity for each date and the row where it occurs:

[ud,~,jj] = unique(date);
N = numel(ud);
val = zeros(N,1);
row = zeros(N,1);
for ii = 1:N
    group_idx = find(jj == ii);
    [val(ii),temp_idx] = min(time_to_maturity(group_idx));
    row(ii) = group_idx(temp_idx);
end

fprintf('Date %d: minimum TimeToMaturity is %02d, which occurs in row %02d\n',[ud val row].');

Date 1: minimum TimeToMaturity is 18, which occurs in row 04
Date 2: minimum TimeToMaturity is 03, which occurs in row 10
Date 3: minimum TimeToMaturity is 22, which occurs in row 12
Date 4: minimum TimeToMaturity is 39, which occurs in row 18