standard deviation of same values in a matrix

Hello,

I couldn't find anything which could help me with my problem.

I have a matrix (n x 2) like shown below:

I want to calculate the standard deviation of column 2 for all records which have the same valaue in column 1. So I get this:

Is there a smart way to do this? Maybe is several steps?

Thanks!

Answer 1

[the cyclist]

The accumarray function is designed for this:

M = [5 0.30;
     5 0.35;
     7 0.50;
     7 0.51;
     9 0.98;
     9 0.87;
     9 0.71];

[uniqueM,idxToUnique,idxFromUniqueBackToAll] = unique(M(:,1));

S = accumarray(idxFromUniqueBackToAll,M(:,2),[],@std)

stdDevM = [uniqueM,S]

[Fabi Boro]

Thank you! works quite well!

[the cyclist]

The best form of thanks is accepting the solution, which rewards the person who helped you, and also points future users to good answers.

Answer 2

[John D'Errico]

Download consolidator , from the file exchange. One line then.