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Matrix problem for same values of column

Asked by Anu Sharma on 2 Sep 2019
Latest activity Answered by Andrei Bobrov
on 2 Sep 2019
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.

  1 Comment

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?

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2 Answers

Answer by Stephen Cobeldick on 2 Sep 2019
Edited by Stephen Cobeldick on 2 Sep 2019
 Accepted Answer

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

  3 Comments

please tell me, In which variable ,output matrix is storing.
"In which variable ,output matrix is storing. "
B
Thankyou so much..

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Answer by Andrei Bobrov
on 2 Sep 2019

[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');

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