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Re: Variable number of arguments

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113342] Re: Variable number of arguments
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sun, 24 Oct 2010 06:06:15 -0400 (EDT)

It's not clear what you want done if the multiple elements are themselves lists or the arguments are a mix of lists and individual elements. The following approach will sum all the individual elements no matter how they are structured.

funnySum1[x__] := Plus @@ Flatten[{x}]

{funnySum1[1, 2, 3, 4],
 funnySum1[{1, 2, 3, 4}],
 funnySum1[1, 2, {3, 4}],
 funnySum1[{1, 2}, {3, 4}],
 funnySum1[{{1, 2}, {3, 4}}]}

{10, 10, 10, 10, 10}

funnySum2[x__] := Total[Flatten[{x}]]

{funnySum2[1, 2, 3, 4],
 funnySum2[{1, 2, 3, 4}],
 funnySum2[1, 2, {3, 4}],
 funnySum2[{1, 2}, {3, 4}],
 funnySum2[{{1, 2}, {3, 4}}]}

{10, 10, 10, 10, 10}

funnySum3[x__] := Tr[Flatten[{x}]]

{funnySum3[1, 2, 3, 4],
 funnySum3[{1, 2, 3, 4}],
 funnySum3[1, 2, {3, 4}],
 funnySum3[{1, 2}, {3, 4}],
 funnySum3[{{1, 2}, {3, 4}}]}

{10, 10, 10, 10, 10}


Bob Hanlon

---- Sam Takoy <sam.takoy at yahoo.com> wrote: 

=============
Hi,

I'm looking for help writing functions with variable number of arguments.

For example, how do I accomplish the (rather artificial) task of writing 
the function FunnySum that:
- When called with multiple arguments, sums them
- When called with a list, sums the elements of the list

I was hoping that the FunnySum1 below would work, but it doesn't 
multiple arguments. FunnySum2 works, but is that the best solution?

FunnySum1[k__] := Apply[Plus, If[ListQ[k], Sequence[k], k]]
FunnySum1[{1, 2, 3, 4, 5, 6}]

FunnySum2[k__] := Plus[k]
FunnySum2[k_List] := Apply[Plus, Sequence[k]]
FunnySum2[1, 2, 3, 4, 5, 6]
FunnySum2[{1, 2, 3, 4, 5, 6}]

Many thanks in advance,

Sam



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