Sort matrix based on unique values in one column

Hi guys. I can't seem to overcome my problem. I have a matrix with 5 columns and a lot of rows. I need to sort the whole matrix based on unique values in column 1. How do I do that? So I need to find the unique values (its a timestamp from my experiment) in column one and also the corresponding values in the rest of the columns and everything else needs to be deleted. Thanks!

Answer 1

[Stephen23]

[~,idx] = sort(mat(:,1)); % sort just the first column
sortedmat = mat(idx,:);   % sort the whole matrix using the sort indices

You can even do the same thing with unique to get the rows corresponding to unique values in the first column:

[~,idu] = unique(mat(:,1))
uniquerows = mat(idu,:);

Note that unique has options for controlling the order of its outputs, and whether it takes the first or last matching element. You should check its documentation and pick the best options for you requirements.

[Guillaume]

That's a bit overkill. The same can be achieved simply with:

sortedmat = sortrows(mat, 1); %you don't even need the ,1 for 1st column

However, I don't think that's what the OP is asking (since he mentions using unique values).

[Ida Rosendahl]

Ah, thanks a lot. Using 'unique' instead of 'sort' in your answer totally solved my problem.

[Krishna Nikhil Sumanth Behara]

Awesome..it worked for me too! Thanks a lot Guillaume

[marjan monfared]

Thank you, it was lifesaver

[chaman lal dewangan]

Thanks. It sorts correctly. I am happy.

[Mike King]

Thank You

[Adam Ward]

Thank you so much!

[Emma Warner]

Just what I was looking for. Thank you!

[IVAN JIMENEZ]

you saved my life, thnks

[ömer canözü]

thank you so much

[Ranjith K]

[~,idu] = unique(mat(:,1))

how to mention the name inside of 1 2 ....10

For example B1 B2 B3.............B10

Answer 2

[Guillaume]

I'm not sure what you mean by "and everything else needs to be deleted". Does that means that rows with identical first column also have the exact same values for all the other columns, or that you want to somehow merge these identical rows into just one?

Assuming all duplicate rows are identical (but then why would you say unique values in one column?):

b = unique(a, 'rows');

Assuming you want to just keep one arbitrary row out of the ones that have identical first column:

[~, rows] = unique(a(:, 1));
b = a(rows, :);

If you want to somehow merge the duplicate rows, it probably can be done but you need to give more details.

[STAVRINI TSANGARI]

how can I get the average of the two duplicate columns?

Answer 3

[Mohammad Bhat]

sir, If we want to keep only maximum value besides second unique column value...