MATLAB Answers

0

How to sort a matrix's columns by using indexes

Asked by phdcomputer Eng on 25 Aug 2019
Latest activity Edited by dpb
on 25 Aug 2019
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

Sign in to comment.

2 Answers

Answer by Bruno Luong
on 25 Aug 2019

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);

  0 Comments

Sign in to comment.


Answer by dpb
on 25 Aug 2019
Edited by dpb
on 25 Aug 2019

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
Why? 'Cuz I didn't read the Q? carefully enough... :)
Good catch, Bruno!

Sign in to comment.