sort matrix by absolute value

How do I sort a matrix by absolute value and display its original value with +,- sign?

Answer 1

[DGM]

Consider the case for a vector:

A=randi(19,[10 1])-10
[~,idx]=sort(abs(A))

Asorted=A(idx)

For other arrays, you'll have to decide how exactly you want to sort it, and do the indexing accordingly.

[Poorva]

clc
clear
% generating the table of rows and columns
row = input('Enter number of rows: ');
col = input('Enter number of columns: ');
C = zeros(row ,col);
%taking values from user of matrix
for s = 1:row
 
    for l = 1:col
      str = ['Enter element in row ' num2str(s) ', col ' num2str(l) ': '];
      C(s,l) = input(str);
    end
end
%taking absolute values of all elements
D=abs(C);
%sorting the rows in descending order


[T,I]=sort(D,2,'descend');

This is my code. Please help me with this, Matrix C has the original input from user in +,- sign, D has the absolute value of C, T gives the sorted matrix but all in + sign ,but I want the sorted result with both +,- sign as the input given by user.

e.g C= [ 1 -8

-4 7]

D=[ 1 8

4 7]

T=[8 1

7 4]

i want the result as res= [-8 1

7 -4]

[DGM]

If you want to sort descending on dim2, my method becomes more cumbersome because of how the index array is organized as row vector indices instead of array indices.

% you could do this without a loop
% but this is less obfuscated
[T,idx]=sort(abs(C),2,'descend');
for r=1:row % because we're sorting on dim2
	T(r,:)=C(r,idx(r,:));
end
T

If you're using a sufficiently recent version, you can just use Steven's suggestion from his answer, which is much more concise.

T=sort(C,2,'descend','comparisonmethod','abs')

For your purposes these two methods are probably both fine, but they do handle duplicate values differently.

[Poorva]

Thank you ....I got it now and the code is working well.

[Poorva]

[y, idx2] = sort(D,2,'descend');
  sx        = size(C);
  index     = sub2ind(sx, repmat((1:sx(1)).', 1, sx(2)), idx2);
  y2        = C(index);
  res=array2table(y2)

Answer 2

[Steven Lord]

Specify the 'ComparisonMethod' name-value pair argument.

rng default
A = randi([-10 10], 5, 5)

A = 5×5

7 -8 -7 -8 3 9 -5 10 -2 -10 -8 1 10 9 7 9 10 0 6 9 3 10 6 10 4

[values, locations] = sort(A(:), 'ComparisonMethod', 'abs');
[values.'; locations.']

ans = 2×25

0 1 -2 3 3 4 -5 6 6 7 7 -7 -8 -8 -8 9 9 9 9 10 10 10 10 10 -10 14 8 17 5 21 25 7 15 19 1 23 11 3 6 16 2 4 18 24 9 10 12 13 20 22

[DGM]

Do you know about when that option was introduced? I'm guessing it was some time around 2018, but release notes are vague and I only know it's not in R2015b.

[Poorva]

thank you steven ....my code is working.