Suppose I have defined some function (This is arbitrary)


I want to apply this F for a given huge list of sets

 {{alpha1, {a1,b1,c1}}, {alpha2, {a2,b2,c2}}, {alpha3, {a3,b3,c3}}}

Of course, I can plug this individually, but is there any smart way of plugging these lists into the function $F$ defined above?

For example, I know,

   F /@ List[a, b, c]


 {F[a], F[b], F[c]}

So my first trial was just

  F /@ {{alpha1, {a1, b1, c1}}, {alpha2, {a2, b2, c2}}, alpha3, {a3, b3, c3}}}

But this gives an extra list outside and inside for $\{a1,b1,c1\}$. i.e.,

 {F[{alpha1, {a1, b1, c1}}], F[{alpha2, {a2, b2, c2}}], F[{alpha3, {a3, b3, c3}}]}

How one can do it wisely?

My solution is given as follows :

 Map[F[#[[1]], Sequence@@#[[2]]] &, {alpha1, {a1, b1, c1}}, {alpha2, {a2, b2, 
c2}}, {alpha3, {a3, b3, c3}}}]

then it produces desired one

  • 3
    $\begingroup$ If you rewrite the function as F[{alpha_,{a_,b_,c_}}]:=List[alpha,a+b+c], you can simply map it over your list. $\endgroup$ May 19, 2023 at 10:56

2 Answers 2

F[alpha_, a_, b_, c_] := List[alpha, a + b + c]

Let's start with what you didn't ask: If you had:

y = {{alpha1, a1, b1, c1}, {alpha2, a2, b2, c2}, {alpha3, a3, b3, c3}}

F @@@ y

would give:

{{alpha1, a1 + b1 + c1}, {alpha2, a2 + b2 + c2}, {alpha3, a3 + b3 + c3}}

For the case in the OP with an extra set of braces:

x = {{alpha1, {a1, b1, c1}}, {alpha2, {a2, b2, c2}}, {alpha3, {a3, b3, c3}}}

F[#1, Sequence @@ #2] & @@@ x

would deliver the same result.

{{alpha1, a1 + b1 + c1}, {alpha2, a2 + b2 + c2}, {alpha3, a3 + b3 + c3}}

Another variation using operator forms, where I can Flatten the arguments first and then use Apply down the list.

  • $\begingroup$ .. which I now realize is close enough to your recent edit to count as plagiarism. $\endgroup$
    – Syed
    May 19, 2023 at 9:41
  • $\begingroup$ Thanks for the quick answer! Can you explain to me what is the difference for @, @@, @@@? As far as I know @@ is nothing but a replacement, i.e., Sequence@@List[a,b,c]=Sequence[a,b], and @ can be used with /@, Map function, but I am not sure about @@@ x which you used in the answer! $\endgroup$
    – phy_math
    May 19, 2023 at 9:47
  • 1
    $\begingroup$ Define: t = {{a}, {b}, {c}, {d}}; and then try: f@t, f /@ t, f @@ t and f @@@ t on it. To gain insight on how the @@ changes an expression, look at TreeForm. $\endgroup$
    – Syed
    May 19, 2023 at 10:00

Point-free style:

list = {{alpha1, {a1, b1, c1}}, {alpha2, {a2, b2, c2}}, {alpha3, {a3, b3, c3}}};
Apply[F]@*Flatten /@ list

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