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How to sort a matrix's columns by using indexes

Asked by phdcomputer Eng on 25 Aug 2019 at 17:17
Latest activity Edited by dpb
on 25 Aug 2019 at 18:06
I wrote some codes to sort an array (a) descendingly. I want to use the indexes (indA) to sort the data matrix's columns.
close all;
clc
load lung.mat
data=lung;
[n,m]=size(data);
l=1;
t=1;
data1=[];
data2=[];
for i=1:n
if data(i,m)==1
data1(l,:)=data(i,:);
l=l+1;
else
data2(t,:)=data(i,:);
t=t+1;
end
end
if t>l
data1(l:t-1,:)=0;
else
data2(t:l-1,:)=0;
end
for i=1: m
thisCol1=data1(:,i);
thisCol2=data2(:,i);
a(i)=fHammingDist(thisCol1,thisCol2);
end
[A,indA]=sort(a,'descend');
I'll be very greatfull to have your opinions how to sort a matrix's columns by using an array of indexes.
Thank you

  1 Comment

Are you sure to compute the distance of the last column which seems to contain special values
...
if data(i,m)==1
...
end
...
for i=1: m
...
a(i)=fHammingDist(thisCol1,thisCol2);
end

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2 Answers

Answer by Bruno Luong
on 25 Aug 2019 at 17:35

Short answer
data = data(:,indA);
Long answer
load lung.mat
data=lung;
b = data(:,end) == 1;
data1 = data(b,:);
data2 = data(~b,:);
n1 = size(data1,1);
n2 = size(data2,1);
if n1 < n2
data1(n2,1) = 0;
elseif n2 < n1
data2(n1,1) = 0;
end
a = arrayfun(@(j) fHammingDist(data1(:,j),data2(:,j)), 1:size(data,2));
[A,indA] = sort(a,'descend');
data1 = data1(:,indA);
data2 = data2(:,indA);
data = data(:,indA);

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Answer by dpb
on 25 Aug 2019 at 17:41
Edited by dpb
on 25 Aug 2019 at 18:06

See
doc sortrows
Not clear which array it is you wish sorted but mayhaps can accomplish directly -- altho the auxiliary array and distances may be needed to have been computed, not knowing exactly the problem trying to solve.
But, given the index vector you've built, simply
A=A(indA,:);
if we presume this mystery array is 'A' will rearrange rows in that order.
ERRATUM:
As Bruno points out, I mixed metaphors/switched horses midstream...
A=A(:,indA);
to sort the columns instead, of course.

  2 Comments

Why do you rearrange rows with sorted column indexes?
dpb
on 25 Aug 2019 at 18:05
Why? 'Cuz I didn't read the Q? carefully enough... :)
Good catch, Bruno!

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