how to delete repeated rows in a table?

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Jayden Yeo
Jayden Yeo on 24 Sep 2021
Commented: Jayden Yeo on 27 Sep 2021
I have an array M below. There are some repeated values in column 1. I would like to write a code that deletes all the rows that have repeated values in column 1. The final answer should be [518640 5.959; 522225 8.988].
This is a sample dataset. My actual data has more than 50,000 rows, and I need to delete all the repeated data. Thanks.
M = [518460 3.322; 518460 -12.984; 518520 3.798; 518520 -10.28; 518580 7.763; 518580 16.851; 518640 5.959; 522225 8.988];

Accepted Answer

per isakson
per isakson on 24 Sep 2021
Edited: per isakson on 27 Sep 2021
Test this
%%
M = [518460 3.322; 518460 -12.984; 518520 3.798; 518520 -10.28; 518580 7.763; 518580 16.851; 518640 5.959; 522225 8.988];
%%
[~,ixu] = unique( M(:,1), 'stable' );
M(ixu,:)
ans = 5×2
1.0e+05 * 5.1846 0.0000 5.1852 0.0000 5.1858 0.0001 5.1864 0.0001 5.2222 0.0001
In response to comment
If everything fails, try a for-loop
for jj = 1 : size(M,1)
ixm = find( M(jj,1) == M(:,1) );
if numel(ixm) >= 2
M(ixm,1) = nan;
end
end
M( isnan(M(:,1)), : ) = []
M = 2×2
1.0e+05 * 5.1864 0.0001 5.2222 0.0001
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More Answers (1)

Walter Roberson
Walter Roberson on 27 Sep 2021
format long g
M = [518460 3.322; 518460 -12.984; 518520 3.798; 518520 -10.28; 518580 7.763; 518580 16.851; 518640 5.959; 522225 8.988]
M = 8×2
1.0e+05 * 5.1846 0.0000 5.1846 -0.0001 5.1852 0.0000 5.1852 -0.0001 5.1858 0.0001 5.1858 0.0002 5.1864 0.0001 5.2222 0.0001
[~, ia] = unique(M(:,1), 'stable');
M = M(ia,:)
M = 5×2
1.0e+05 * 5.1846 0.0000 5.1852 0.0000 5.1858 0.0001 5.1864 0.0001 5.2222 0.0001

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