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MathGroup Archive 2006

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Re: Sorting Rows of a Matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg65129] Re: Sorting Rows of a Matrix
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Wed, 15 Mar 2006 06:29:10 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <dv69a6$o6l$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Gregory Lypny wrote:
> Hello everyone,
> 
> How can I sort the rows of a matrix by using one or more of the  
> columns as sort keys just like in a spreadsheet?  For example, if  
> matrix M is 12 x 2 with numbers in the first column and unordered  
> month numbers in the second, how would I order the rows by month?
> 
> 	Regards,
> 
> 		Greg
> 
Hi Gregory,

Here is an example using the *Ordering* built-in function:

In[1]:=
m={{1,a},{2,d},{3,c},{4,e},{5,b},{6,f}};

In[2]:=
m//MatrixForm//OutputForm

Out[2]//OutputForm=
1   a

2   d

3   c

4   e

5   b

6   f

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

Out[3]=
{{1,a},{5,b},{3,c},{2,d},{4,e},{6,f}}

In[4]:=
m//MatrixForm//OutputForm

Out[4]//OutputForm=
1   a

5   b

3   c

2   d

4   e

6   f

Best regards,
/J.M.


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