Re: Pattern Matching Problem

• To: mathgroup at smc.vnet.net
• Subject: [mg43394] Re: Pattern Matching Problem
• From: bobhanlon at aol.com (Bob Hanlon)
• Date: Tue, 16 Sep 2003 04:35:44 -0400 (EDT)
• References: <bihp1v\$b3u\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```I would take a different approach:

ClearAll[f,a,b,c,w,x,y,z,sep];

sep[expr_] := Module[
{tm = List@@expr, at},
at = Select[tm,AtomQ];
Tr/@Prepend[
Split[
Sort[Complement[tm,at],
#1[[2]]<#2[[2]]&],
#1[[2]]==#2[[2]]&],
at]];

expr=a+b+c+f[w,2]+f[w,3]+x+f[x,2]+f[x,3]+y+f[y,2]+f[z,2];

sep[expr]

{a + b + c + x + y, f[w, 2] + f[x, 2] + f[y, 2] + f[z, 2],
f[w, 3] + f[x, 3]}

Bob Hanlon

In article <bihp1v\$b3u\$1 at smc.vnet.net>, "Ersek, Ted R"
<ErsekTR at navair.navy.mil> wrote:

<< Consider the following:

In[1]:=
ClearAll[f,a,b,c,w,x,y,z];
expr=a+b+c+f[w,2]+f[w,3]+x+f[x,2]+f[x,3]+y+f[y,2]+f[z,2];

Can somebody suggest a general way to seperate the terms above into like
groups. By "like" I mean having the same second argument for (f).  So for
this example I want to get

{a+b+c+x+y,  f[w,2]+f[x,2]+f[y,2]+f[z,2],   f[w,3]+f[x,3]}

The pattern matcher should be able to do this because Plus has attributes
Flat and Orderless.  However I can't find a way to make it happen.

```

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