       Re: Help with Delete cases

• To: mathgroup at smc.vnet.net
• Subject: [mg116242] Re: Help with Delete cases
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Tue, 8 Feb 2011 05:05:34 -0500 (EST)

```list = Range;

sol1 = With[{m = 5, p = 7},
DeleteCases[list, _?(Mod[# - m (m + 1)/2, p] == 0 &)]];

sol2 = With[{m = 5, p = 7},
Cases[list, Except[_?(Mod[# - m (m + 1)/2, p] == 0 &)]]];

sol3 = With[{m = 5, p = 7},
Cases[list, _?(Mod[# - m (m + 1)/2, p] != 0 &)]];

sol4 = With[{m = 5, p = 7},
Select[list, Mod[# - m (m + 1)/2, p] != 0 &]];

sol5 = With[{m = 5, p = 7},
list //. _?(Mod[# - m (m + 1)/2, p] == 0 &) :> Sequence[]];

sol1 == sol2 == sol3 == sol4 == sol5

True

3003 - Length[sol1]

429

Bob Hanlon

---- KenR <ramsey2879 at msn.com> wrote:

=============
I have a list= Range  I want to delete cases of n = m(m+1) mod P
from the list, but Delete cases only deletes cases matching a pattern,
i.e.

list = DeleteCases[list,Mod[N - m(m+1)/2,P] = 0] will definitely not
work.  I want to keep list, as the same identifier, throughout since
this is within a looping process. Any suggestions?

```

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