Sorting a list and finding an array of indices that sorts the list

Question

How can I sort a list and also get a list of indices that sort this list? For example: primary list is a

a={1,4,6,7,0,2};

sorted list is b

b={7,6,4,2,1,0}

and also return list c

c={4,3,2,6,1,5}

J. M. · Accepted Answer · 2012-06-24 11:57:57Z

up vote 9 down vote accepted

To get list b, you need Sort[]: Sort[{1, 4, 6, 7, 0, 2}, GreaterEqual].

To get list c, you need Ordering[]: Ordering[{1, 4, 6, 7, 0, 2}, All, GreaterEqual].

answered Jun 24 '12 at 11:57

J. M.♦
27.4k658130

1

+1, Beat me by 20 seconds :-) – Heike Jun 24 '12 at 11:59

@Heike: I guess there is such a thing as being in the right place at the right time... :) – J. M.♦ Jun 24 '12 at 12:00

@J.M. : Thank you – xazar Jun 24 '12 at 12:03

5

Also, if you need both, you might first do Ordering and then b=a[[c]] – Rojo Jun 24 '12 at 14:00

@Rojo: that's a good point with respect to saving sorting effort. :) – J. M.♦ Jun 24 '12 at 14:04

1 Answer