keeping track of the original indices of an array after sorting

I have an array let's say A=[5 4 1 2 3]. Now I have sorted these arrays in ascending order.So the resulting array will now be [1 2 3 4 5]. I use sort(A,'ascend') function to sort this. The question is how can I get the indices of the original array with respect to my new array. originally my indices were 1,2,3,4,5 for corresponding values of 5,4,1,2,3 and now the indices have changed to 3,4,5,2,1. How can I get these indices efficiently in Matlab?

[Stephen23]

The documentation clearly explains that the function sort has two outputs... the second output are the indices that you are after.

http://www.mathworks.com/help/matlab/ref/sort.html

Answer 1

[Mischa Kim]

Md, simply use

[B,I] = sort(A,'ascend') 
B =
     1     2     3     4     5
I =
     3     4     5     2     1

[chandra Naik]

Effective logic, Thank you

Answer 2

[Andy]

and B = A(I), according to documentation, isn't it?

I get following:

>> x = [ 1 3 2 7; 4 3 2 1]

x =

     1     3     2     7
     4     3     2     1

>> [y,i] = sort(x,2)

y =

     1     2     3     7
     1     2     3     4

i =

     1     3     2     4
     4     3     2     1

>> y1 = x(i)

y1 =

     1     3     4     3
     3     3     4     1

I see y1 is different from y ...

[Stephen23]

"and B = A(I), according to documentation, isn't it?"

The documentation states "if A is a vector, then B = A(I)." Is your input a vector? NO. However you can esaily read the rest of the documentation, where it explains the output for matrices and arrays: "The index vectors are oriented along the same dimension that sort operates on. For example, if A is a 2-by-3 matrix, then [B,I] = sort(A,2) sorts the elements in each row of A. The output I is a collection of 1-by-3 row index vectors describing the rearrangement of each row of A."

And your data shows this clearly:

 i =
     1     3     2     4
     4     3     2     1

Have a look: do you see that these are the indices along each row, which is exactly what the documentation states that you would get. It means you cannot use A(I) syntax. You could use sub2ind though.

[Adam]

https://uk.mathworks.com/matlabcentral/answers/333359-using-a-matrix-as-an-index-to-another-matrix

Answer 3

[Leelakrishna Vuriti]

how to arrange the values in ascending order along with its corresponding index change ? what is the command for this ? help me out !