Matrix problem for same values of column

A=[29.78         5	 8
   24.97         8	11
   22.98         4	12
   21.05	12	13
   24.78         1	16
   25.53	26	29
   21.43	 2	32
   29.94	11	33
   29.57	15	35
   28.43	17	36
   11.49        23	37
   13.69	37	38
   26.97	28	39
   16.25	25	40
   27.36	36	41
    4.24  	18	42
   19.39	39	44
   29.93	16	45
   25.83	30	46
   26.09	40	47
   27.58	24	48
   28.61	41	49
   29.41	48	50]

and i want

output =[22.98    4   12
         25.53   26   29
         21.43    2   32
         29.94   11   33
         29.57   15   35
         28.43   17   36
         13.69   37   38
         26.97   28   39
          4.24   18   42
         29.93   16   45
         25.83   30   46
         26.09   40   47
         28.61   41   49
         29.41   48   50 ]

No value in column 2, 3 get repeated and in case of repeated value in any of the column(2,3) the higest value of column 1 is as the output.

For example, in row 1, 2 and 8. column (2,3) have values as

[ 5  8
  8 11
 11 33]

Among these 3 rows row 8, ie. [29.94 11 33] have the highest value so only this row will be the output. all other row like [29.78 5 8] and [24.97 8 11]will be elimanted.

simillarly,

for row 3 = [22.98 4 12]

And 4 = [21.05 12 13]

row 3= [22.98 4 12]

will be output and row 4 will get eliminated.

[Stephen23]

Is the row

28.43   17   36

correct in your example output array? Following your explanation, these rows are one group:

28.43	17	36
...
27.36	36	41
...
28.61	41	49

of which the last row has the highest values in the first column (and the last row is in your output array). But why do you keep the first row as well?

Answer 1

[Stephen23]

N = size(A,1);
X = ones(N,1); % group numbers
Z = true(N,1); % logical index
V = 1; % group number
for k = 2:N % for each row...
    Y = A(k,2)==A(1:k-1,3); % check if any matching rows.
    if any(Y)
        X(k) = X(Y); % copy group number (assumed scalar).
        W = X(k)==X(1:k-1); % logical index of that group.
        if all(A(k,1)>A(W,1))
            Z(W) = false; % current val > prev vals.
        else
            Z(k) = false; %  prev val > current val.
        end
    else % no matching rows:
        V = V+1; % increment group number.
        X(k) = V;
    end
end
B = A(Z,:) % output matrix

Giving:

B =
        22.98            4           12
        25.53           26           29
        21.43            2           32
        29.94           11           33
        29.57           15           35
        13.69           37           38
        26.97           28           39
         4.24           18           42
        29.93           16           45
        25.83           30           46
        26.09           40           47
        28.61           41           49
        29.41           48           50

[Anu Sharma]

please tell me, In which variable ,output matrix is storing.

[Stephen23]

"In which variable ,output matrix is storing. "

B

[Anu Sharma]

Thankyou so much..

Answer 2

[Andrei Bobrov]

[m,n] = size(A);
B = [(1:m)',A(:,2:3)];
k = B(1,2:3);
ii = 1;
C{1} = [];
while ~isempty(B)
    i0 = ismember(B(:,2:3),k);
    lo = any(i0,2);
    if any(lo)
        C{ii} = [C{ii};[repmat(ii,nnz(lo),1),B(lo,1)]];
        k = B(xor(i0(:,1),i0(:,2)),2:3);
        B = B(~lo,:);
    else
        ii = ii + 1;
        k = B(1,2:3);
        C{ii} = [];
    end
end
iii = cat(1,C{:});
T = array2table(A);
T = T(iii(:,2),:);
T.g = iii(:,1);
T = sortrows(T,{'g','A1'},{'ascend','descend'});
T = rowfun(@(x,y,z)[x(1),y(1),z(1)],T,'GroupingVariables','g');