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I've been trying some different approach but all are not working:

I've got 2 polls, the first with 2 options (and 2 list of people which voted each option), the second with 3 options (and 3 list of people). pollA = {pMenoDi25Anni, pPiùDi25Anni}; pollB = {pLavoroFullTime, pStudioEBasta, pLavoroPartTime};

I'd like to calculate the intersection between each element of pollB (each of which is a set) and pMenoDi25Anni.

I've tried using Thread

In: Thread[Intersection[
  pMenoDi25Anni, {pLavoroFullTime, pLavoroPartTime, pStudioEBasta}] ]
Out: {pMenoDi25Anni \[Intersection] pLavoroFullTime, 
 pMenoDi25Anni \[Intersection] pLavoroPartTime, 
 pMenoDi25Anni \[Intersection] pStudioEBasta}

enter image description here

It looks like exactly what I am looking for , but after assigning the real values to the this variables I get an unexpected result pLavoroFullTime = {1, 2}; pLavoroPartTime = {3, 4}; pStudioEBasta = {5, 6}; pMenoDi25Anni = {1, 3, 5};

In: Thread[Intersection[ pMenoDi25Anni, {pLavoroFullTime, pLavoroPartTime, pStudioEBasta}] ] Out: {}

Can you explain me what's going on?

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1 Answer 1

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In MMA arguments are evaluated before feeding them to a function. This means

Intersection[pMenoDi25Anni, {pLavoroFullTime, pLavoroPartTime, 
  pStudioEBasta}]

is evaluated before feeding to Thread. Now, Intersection takes lists as arguments. This is fine for the first argument, but the second argument is a list of lists. Therefore, the intersection is empty.

What you want is "Map", for short "/@":

Clear[pLavoroFullTime, pLavoroPartTime, pStudioEBasta, pMenoDi25Anni];
pLavoroFullTime = {1, 2}; pLavoroPartTime = {3, 
  4}; pStudioEBasta = {5, 6}; pMenoDi25Anni = {1, 3, 5};
Intersection[pMenoDi25Anni, #] & /@ {pLavoroFullTime, pLavoroPartTime,
   pStudioEBasta}

(*{{1}, {3}, {5}}*)
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  • $\begingroup$ Thanks a lot. To better understand the Wolfram Language, is there any method to generalize this intersection to any List of Lists using Tuples or Outer? mathematica.stackexchange.com/questions/257645/… @Daniel Huber $\endgroup$
    – Revious
    Commented Nov 3, 2021 at 10:34
  • $\begingroup$ I mean Intersection[{pMenoDi25Anni, pMoreThan25YearsOld}, {pLavoroFullTime, pLavoroPartTime, pStudioEBasta}] the 1st element of the 1st list intersect 1st element of second list, then with the second, then with the 3rd and so on $\endgroup$
    – Revious
    Commented Nov 3, 2021 at 10:36
  • 1
    $\begingroup$ Look at "MapThread" $\endgroup$
    – Daniel Huber
    Commented Nov 3, 2021 at 10:38
  • $\begingroup$ thanks a lot!!! $\endgroup$
    – Revious
    Commented Nov 3, 2021 at 11:18

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