Suppose you have the list list={a,Sin[b+c],d+c}. What I want is to transform all elements of list with head Plus into a list again, so that the desired output would be {a,Sin[b+c],d,c}. Simply using List@@ or /.Plus->List will for sure not work since it either transforms all heads (including those that should be left unchanged) or e.g. replaces function arguments.

So what is a neat way to accomplish this potentially very easy task?

  • 1
    $\begingroup$ Does the order matter, i.e., {a, Sin[b+c],c,d} vs your result. $\endgroup$ – ciao Aug 11 '15 at 2:07
  • $\begingroup$ @ciao The order does not matter. All elements will be symbolic terms that will be summed up at the very end of a long computation. But thanks for pointing this out - I didn't think about the importance while posting the question :) $\endgroup$ – Lukas Aug 11 '15 at 2:45
  • $\begingroup$ Then Jens' answer is the way to go... $\endgroup$ – ciao Aug 11 '15 at 2:50

How about this?

list = {a, Sin[b + c], d + c};

Replace[list, HoldPattern[Plus[x__]] :> Sequence[x], 1]

(* ==> {a, Sin[b + c], {c, d}} *)

Here, HoldPattern is needed to prevent the Plus from being swallowed. I use Replace because it allows me to specify the level 1 at which the replacement is to occur.

  • $\begingroup$ Not what they're after... c d s/b sequence... $\endgroup$ – ciao Aug 11 '15 at 2:12
  • $\begingroup$ @Ciao Oh, right... $\endgroup$ – Jens Aug 11 '15 at 2:13
  • $\begingroup$ And if order matters.... whole 'nother ball-o-wax, +1 though ;-) $\endgroup$ – ciao Aug 11 '15 at 2:14
  • $\begingroup$ @ciao Thanks - you're right that the order could be tricky because you have to deal with the lexical rules. $\endgroup$ – Jens Aug 11 '15 at 2:16
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    $\begingroup$ You can also do Replace[list, Plus -> Sequence, {2}, Heads -> True] $\endgroup$ – mfvonh Aug 11 '15 at 3:01

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