Find n minimum values in an array?
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I have an array, I need to be able to select 2, or 4 or so on 'n' minimum (smallest) values from the specific array? I know i can use 'min' function but this only gives one smallest value. I do not want to sort the array in order and pick values. is there another way ?????
3 commentaires
Nicholas Ayres
le 21 Août 2020
The "optional second output" of sort is the index order.
[sortedVals,indexes] = sort(myvals);
So
myVals = [1 0.1 7 10 4];
[sortedVals,indexes] = sort(myVals);
gives
sortedVals = [0.1 1 4 7 10]
indexes = [2 1 5 3 4]
Figured I'd pop this here in case anyone else comes along with the same question. :)
Réponse acceptée
Titus Edelhofer
le 15 Avr 2015
Hi,
if you don't want to sort, and n is not too large, you could remove the index, something like
x = rand(1000, 1);
n = 5;
val = zeros(n,1);
for i=1:n
[val(i),idx] = min(x);
% remove for the next iteration the last smallest value:
x(idx) = [];
end
Titus
5 commentaires
Rik
le 8 Juil 2019
I know this is an old thread, but still:
Even replacing x(idx) with NaN instead of removing the entry doesn't really improve the speed. This might be dependent on the release and of the size of the input array.
zaid tahir
le 5 Mar 2021
@Titus Edelhoferthanks for the code. Helped make a very complex problem, very simple.
Plus de réponses (4)
Jan
le 23 Jan 2017
While sorting is the best approach to get the data, you can easily obtain an unsorted result:
n = 2;
[xs, index] = sort(x);
result = x(sort(index(1:n)))
1 commentaire
Chris Volpe
le 1 Fév 2023
Seems to me you want to leave out the "sort" call in line 3:
result = x(index(1:n))
Salam Ismaeel
le 30 Août 2018
use: mink() command for R2018a
https://www.mathworks.com/help/matlab/ref/mink.html
3 commentaires
Bill Tubbs
le 22 Juin 2020
This is the correct answer. Thanks!
Example:
>> X = [4 1 2 1 5 4 2];
>> [minValues, idx] = mink(X,3)
minValues =
1 1 2
idx =
2 4 3
Titus Edelhofer
le 15 Avr 2015
Modifié(e) : Titus Edelhofer
le 15 Avr 2015
Hi,
if it's not floating point but integers (so no problem with roundoff),you could do the following:
x = [1 3 2 4 1 3 5 4 1 3 1]
% find the first 2 min occurrences:
idxMin = find(x==min(x), 2, 'first')
This tells that the smallest value 1 is found at positions 1 and 5. Or are you looking for the n smallest values in the sense, you are looking for the smallest, the second smallest etc.? In this case the answer is simply
n = 2;
xs = sort(x);
% pick the n smallest:
xs(1:n)
Titus
5 commentaires
Titus Edelhofer
le 15 Avr 2015
If this was what you were looking for, then please mark the question as answered ... Thanks, Titus
Luis Gomez
le 30 Août 2022
Modifié(e) : Luis Gomez
le 30 Août 2022
I do it like this,
% k miminum values of a matrix (return the position, not the value)
% not optimized: it just worked for my application.
a = magic(5)
%Copy the original data
aa = a;
%Size of the matrix
[rows columns] = size(a);
%Select the k mininum values
k = 3;
k_mins = zeros(k,1); %to store solution (not really needed)
for i = 1: k
[m, I] = min(a(:));
a(I) = inf;
k_mins(i) = I;
end
k_mins
% to get the [i, j] usual matrix locations for ecah value within k_mins
% for instance, to get the "i,j" indices por first element of k_mins
% vector,
[i j] = ind2sub([rows, columns],k_mins(1))
%the value
aa(i,j)
8 commentaires
Rik
le 30 Août 2022
@Walter, to be honest I always forget that function exists ever since it was introduced in R2017b.
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