Re: Sorting Rows of a Matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg65138] Re: Sorting Rows of a Matrix*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Wed, 15 Mar 2006 06:29:58 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 3/14/06 at 6:00 AM, gregory.lypny at videotron.ca (Gregory Lypny) wrote: >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? There are a number of ways to achieve what you want. One way to do it would be based on the documentation for Sort, i.e., Sort[M, OrderedQ@{#1[[2]],#2[[2]]}&] That is use the second argument for Sort to specify the sort order. Equivalent results can be obtained with M[[Ordering[M[[All,2]]]]] to order by the second column I find for me, this second method runs faster for large arrays. -- To reply via email subtract one hundred and four