CODEWITHSUNDEEP
matlabindexing
w.kamal
w.kamal

Reputation: 3

finding indices of min or max calculated in a range of an array or matrix in matlab

If I have a matrix

A=rand(50,4);

and a matrix of range values like

range=[1 10 15 30 45 50];

and i want to calculate minimum value and its index in all A columns over the range matrix. for example

for i=1 :numel(range)-1
[value index]= find(min(A(range(i):range(i+1),[],1)

if i>1
            index=index+ range(i)+1;       % indx# was calculated onlyin a 
                                              % range of array and not for 
                                             %whole array.Updated here
 end

B_ind(i,:)=index;
B_val(i,:)=value;
end

How can I get indices of min(A) for range(i:i+1) without using a loop approach?

Simply put, matrix 'B' should be like

B(1,column 1:4)=index of min(A (1:10))   in every column

B(2,column 1:4)=index of min(A (11:15))  in every column

B(3,column 1:4)=index of min(A (16:30))  in every column

and so on...

My question is how to do it without a 'for loop'?

Upvotes: 0

Views: 165

Answers (1)

Irreducible
Irreducible

Reputation: 899

One possibility would be:

% generate example data set
A=rand(50,4);
range=[1 10 15 30 45 50];

% generate indexes of interest
tmp_idx= arrayfun(@colon,range(1:end-1),range(2:end),'un',0);
% calculate the min function over the indexes
[min_value,min_idx]=cellfun(@(x) min(A(x,:)), tmp_idx, 'UniformOutput', false);
% get matrix B (with the offset of ranges)
B=cell2mat(min_idx')+(range(1:end-1)+1)';
B(1,:)=B(1,:)-2;

Upvotes: 2

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