Re: sorting a Matrix
- To: mathgroup@smc.vnet.net
- Subject: [mg12278] Re: sorting a Matrix
- From: Paul Abbott <paul@physics.uwa.edu.au>
- Date: Tue, 5 May 1998 03:30:15 -0400
- Organization: University of Western Australia
- References: <6ilpsl$jpo$12@dragonfly.wolfram.com>
Klamser wrote:
> with Sort[{a,f,e,s}] I can sort a Vector (a List). How can I sort a
> Matrix??
>
> In the Help I can find the Information: Sort[{33,76,2,6,17},#1>#2&]
>
> For a Matrix I think it should work like this:
> Sort[{33,76,2,6,17},#1[[#5,#3]]>#2[[#4,#3]]&]
>
> where #3 is the column to be sorted for, and #5 and #4 are the different
> Vectors in the Matrix.
>
> Can somebody help me??
For a random 4x4 matrix, say,
In[1]:= mat = Table[Random[], {4}, {4}] Out[1]= {{0.266234, 0.647371,
0.730429, 0.565464},
{0.00975624, 0.0234279, 0.571189, 0.196294},
{0.171129, 0.27151, 0.820526, 0.760194},
{0.201956, 0.988453, 0.666745, 0.569845}}
Sort, by default uses #1<#2&:
In[2]:= Sort[mat]
Out[2]= {{0.00975624, 0.0234279, 0.571189, 0.196294},
{0.171129, 0.27151, 0.820526, 0.760194},
{0.201956, 0.988453, 0.666745, 0.569845},
{0.266234, 0.647371, 0.730429, 0.565464}}
This has ordered the vectors by the first column. To order by column 3,
In[3]:= Sort[mat, #1[[3]] < #2[[3]] & ] Out[3]= {{0.00975624, 0.0234279,
0.571189, 0.196294},
{0.201956, 0.988453, 0.666745, 0.569845},
{0.266234, 0.647371, 0.730429, 0.565464},
{0.171129, 0.27151, 0.820526, 0.760194}}
Cheers,
Paul
____________________________________________________________________
Paul Abbott Phone: +61-8-9380-2734
Department of Physics Fax: +61-8-9380-1014
The University of Western Australia Nedlands WA 6907
mailto:paul@physics.uwa.edu.au AUSTRALIA
http://www.pd.uwa.edu.au/~paul
God IS a weakly left-handed dice player
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