Re: Sort on vector component

• To: mathgroup at smc.vnet.net
• Subject: [mg122024] Re: Sort on vector component
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Sun, 9 Oct 2011 03:53:28 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com

```On 10/8/11 at 5:36 AM, weh at snafu.de (Dr. Wolfgang Hintze) wrote:

>Given a list

>u = {{2, 12, 7, 21}, {2, 48, 47, 97}, {4, 42, 41, 87}, {6, 8, 1,
>15}, {6, 12, 9, 27}}

>How can I sort it with respect to a given index position i=(1, ...,
>4)?

One way to do this that should be fairly fast using index 3 as an example is:

In[2]:= u[[Ordering[u[[All, 3]]]]]

Out[2]= {{6, 8, 1, 15}, {2, 12, 7, 21}, {6, 12, 9, 27}, {4, 42, 41,
87},
{2, 48, 47, 97}}

Another way would be to use a pure function as the ordering function with Sort. That is:

In[5]:= Sort[u, #1[[3]] < #2[[3]] &]

Out[5]= {{6, 8, 1, 15}, {2, 12, 7, 21}, {6, 12, 9, 27}, {4, 42, 41,
87},
{2, 48, 47, 97}}

```

• Prev by Date: ratnz: Solve
• Next by Date: How long does it take to run the Notebook that makes the mathematica Quintic poster?
• Previous by thread: RE: Sort on vector component
• Next by thread: Re: Sort on vector component