How to use Rules on Sequences?
- To: mathgroup at smc.vnet.net
- Subject: [mg29452] How to use Rules on Sequences?
- From: Detlef Mueller <dmueller at mathematik.uni-kassel.de>
- Date: Wed, 20 Jun 2001 04:36:31 -0400 (EDT)
- Organization: University of Kassel - Germany
- Sender: owner-wri-mathgroup at wolfram.com
Hello,
I am faced to the following Problem:
given a List of Pairs of the Form
L = {{a1,m1},{a2,m2}, ... ,{ai,mi}}
and a Number a, I want to replace the Pair
{a, mj}, if it appears in the List by
{a, mj-1}.
This Job is done by
L /. {{a,_m}->{a,m-1}}.
Now I want to remove an Item of the Form
{a,0} entirely from The List.
Can this be done by applying rules (without
leaving Null-Entrys), or is "Select" the only
Way?
(By the way: L is sorted with respect to the first Elements
of the Sublists, this first elements are unic identifiers.
Another Question is to replace an {a,_m} in L by {a,m+1},
if it exists or else insert {a,1} in the propper
Place - the inverse Operation of the above desribed
one. Suerly not difficult to realize - but what might
be the most efficient Method?)
More general, I wonder, how to replace
a Pattern in a Sequence - for example to change
every occurence of "x_, y_?positive, x_" in a Sequence
by "x,0,x".
Say
Emil[1,2,3,2,0,a,b,c]/.R ---> (Replacing ... 2,3,2 ... )
Emil[1,2,0,2,0,a,b,c]/.R ---> (Replacing ... 0,2,0 ... )
Emil[1,2,0,0,0,a,b,c]/.R (No more changes).
I Fail to write down a syntactically correct rule R to
do this Job.
Greetings
Detlef Mueller