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.