Functional realisation of do-loop

Question

I'm currently optimising my code and I'm using a lot of loops, so I was wondering if there is a smarter or faster way to do things like:
 Do[If[MemberQ[List1[[II]], List2_], AppendTo[Newlist1, List1[[II]]]], {II, Length[List1]}]
I guess using Apply would be better, but since I'm not primary a programmer I would be happy for any help. Thank you!

Roman · Accepted Answer

First question: select those elements in list1 that also appear in list2:
list1 = {a, b, c, d, e, f};
list2 = {e, g, i};
Select[list1, MemberQ[list2, #] &]
(*    {e}    *)

Second question: select those elements in list1 that have a factor that is in list2:
list1 = {a b c d, x y z, m n o};
list2 = {a, r, l, m};
Select[list1, IntersectingQ[List @@ #, list2] &]
(*    {a b c d, m n o}    *)

Alexei Boulbitch · Answer

Try the following, first remove from the first list the elements of the second one:
lst1 = {a, b, c, d, e, f, g};
lst2 = {b, c, g};
Complement[lst1, lst2]
(*  {a, d, e, f}  *)

and then append it to the newList.
Clear[newList];
newList = {AA, BB, CC}; (*This is the initial newList*)
AppendTo[newList, Complement[lst1, lst2]] // Flatten
(*  {AA, BB, CC, a, d, e, f}   *)

Have fun!

Functional realisation of do-loop

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