MATLAB: How to find the max and min amongst a set of grouping variables

maxmin

I have a 150×2 matrix in which the first column contains numbers that can be considered 'grouping variables' and the second column contains values associated with those grouping variables. So a small 6×2 version would look like this
 1 23
 1 29
 1 43
 2 38
 2 22
 2 100
I'd like to find the maximum of the values associated with each grouping variable. Similarly the minimum amongst the values associated with each grouping variable. So the above example would yield an max of 43(for variable 1) and min of 23 (for variable 1). Similarly, max of 100 (for variable 2) and min of 22 (for variable 2). Does anybody know of a similar function or method to achieve this in Matlab?

Best Answer

Since you didn't write if every number will occur in the first column, I allow for "missing" numbers here (it doesn't make a big difference anyway):
a=1+fix(0:.23:8)' ;
b=randi(50,length(a),1);
M=[a b]
nums=unique(M(:,1));
mmin=zeros(max(nums),1);
mmax=zeros(max(nums),1);
for cnt=1:max(nums)
  mmin(nums(cnt))=min(M(M(:,1)==nums(cnt),2));
  mmax(nums(cnt))=max(M(M(:,1)==nums(cnt),2));
end
If every number will occur, nums(cnt)==cnt, so the expressions inside the loop can be simplified a bit.
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