Re: Mathematica 6.0 easier for me ... (small review)
- To: mathgroup at smc.vnet.net
- Subject: [mg76581] Re: Mathematica 6.0 easier for me ... (small review)
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Thu, 24 May 2007 06:06:51 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <f30vpv$mkn$1@smc.vnet.net>
Paul at desinc.com wrote:
[snip]
> 4. At work, I haven't had to resort to other programs because
> Mathematica wasn't the best choice. This is extremely nice. BTW,
> There's a "temporal" advantage with procedural programming that hasn't
> been apparant to me in functional or rule. Still working on it. Maybe
> someone can help. If I have
> lis={{1,10},{2,10},...{9,10},{11,20},{12,20}...{19,20}
>
> How do I use functional and/or rule to determine where the second
> number (lis[[i,2]]) jumped from 10 to 20 to 30 and save the pair.
> Assuming there was noise, I only want to store the first 10->20, then
> look for 20->30 and so on. So in time, I want my search to change as
> I progress through the list. Any input appreciated!
[snip]
The following expression should be a good start:
In[1]:=
lst = {{1, 10}, {2, 10}, {3, 10}, {4, 10}, {8, 10}, {9, 10}, {11, 20},
{12, 20}, {13, 20}, {16, 20}, {17, 20}, {18, 20}, {25, 30},
{26, 30}, {27, 30}, {28, 30}, {29, 30}};
(First[Take[##1, -1]] & ) /@
Drop[Split[lst, Last[#1] == Last[#2] & ], -1]
Out[2]= {{9, 10}, {18, 20}}
Regards,
Jean-Marc