# Sorting array of sym

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Tanmaya on 15 Jul 2024 at 18:21
Commented: Tanmaya on 18 Jul 2024 at 16:51
I get wrong answers in this case. Am I doing anything wrong ?
>> a = sym.empty();
>> a = [a,0,pi,pi/2,-pi/2,pi/4]
a =
[0, pi, pi/2, -pi/2, pi/4]
>> sort(a)
ans =
[0, pi, -pi/2, pi/2, pi/4]
Walter Roberson on 15 Jul 2024 at 19:42
Pi = sym(pi);
a = [-Pi/4 -Pi/3 -Pi/2 -Pi -Pi*3/4 -Pi*2/3 Pi/4 Pi/3 Pi/2 Pi Pi*3/4 Pi*2/3 -Pi*1/5 -Pi*2/5 -Pi*3/5 -Pi*4/5 Pi*1/5 Pi*2/5 Pi*3/5 Pi*4/5]
a =
sort(a)
ans =
a = a(randperm(numel(a)))
a =
sort(a)
ans =
So the sorting results are stable, but they are not obvious.
Tanmaya on 18 Jul 2024 at 16:51
Thanks

Milan Bansal on 15 Jul 2024 at 18:45
Hi Tanmaya
To sort the symbolic array numerically, you can convert the symbolic expressions to their numerical equivalents before sorting. Here's how you can do it:
1. Convert the symbolic expressions to numerical values.
2. Sort the numerical values.
3. Recreate the sorted symbolic array using the indices from the sorted numerical values.
Please refer to the following code snippet to implement the same:
a = sym.empty();
a = [a, 0, pi, pi/2, -pi/2, pi/4];
a = sym(a); % Ensure the array is symbolic
% Convert to numerical values
num_a = double(a);
% Sort the numerical values and get the sorting indices
[sorted_num_a, sort_idx] = sort(num_a);
% Recreate the sorted symbolic array using the indices
sorted_a = a(sort_idx);
disp(sorted_a);
Hope this helps!
John D'Errico on 15 Jul 2024 at 19:59
This is pretty much all you can do, to convert the elements to actual numbers in some form. But there is no value in creating a as a sym.empty first.
a = sym([0, pi, pi/2, -pi/2, pi/4]);
a = sym(a)
a =
You don't need ot go all the way to doubles though. vpa would seem more accurate, and still works.
[~,idx] = sort(vpa(a));
a = a(idx)
a =
Tanmaya on 18 Jul 2024 at 16:50
Thanks

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