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Basically I have a really large output which looks like a long linear equation

$AAA-BAA-CAA+DAA+...-ZZZ$

And I only am concerned about those terms that have a positive coefficient (i.e. a plus in front). The others I can ignore.

How can I get mathematica to ignore those positive-coefficient terms, or at the very least order the list such that the negative coefficient terms are in the front (or back).

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  • $\begingroup$ aaa - bbb + ccc + dd - eee /. Times[-1, __] :> Sequence[]? $\endgroup$
    – kglr
    Aug 24, 2014 at 14:36
  • $\begingroup$ @kguler Wow, works like a charm! Thanks! But I can't parse it easily, how does it work? $\endgroup$
    – quantum_loser
    Aug 24, 2014 at 14:39
  • $\begingroup$ i posted a simpler solution. Regarding how it works, please see ReplaceAll and PatternTest in the docs for many examples. $\endgroup$
    – kglr
    Aug 24, 2014 at 14:48

1 Answer 1

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expr = aaa - 3 bbb + ccc + ddd - eee
expr /. _?Negative :> 0
(* aaa + ccc + ddd *)
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