4
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I have a list of some sort list = {"l1","l2","l3","l4"} and I'd like to count the sum total number of occurrences of n of the elements in the list. This is easily done for one element: Count[list, "l1"] which gives 1. How can I write something like Count[list, "l3" OR "l2" OR "l1"], in this example giving the output 3? I read through the manual for Count and surprisingly couldn't find out how to ask for this.

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Use Alternatives. You aren't getting any help from the Count[] docs because it's more related to Patterns

list = {"l1", "l2", "l3", "l4"};
Count[list, Alternatives["l1", "l2", "l3"]]
(* or abbreviated *)
Count[list, "l1" | "l2" | "l3"]
(*
 3
 3
*)
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1
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Alternately,

Total@((#[[1]][#[[2]]] &) /@ Tuples[{##}]) &[(Function[v, 
Function[u, Length@Select[u, # == v &]]] /@ {"11", "12", 
"13"}), {{"11", "12", "13", "14"}}]
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  • $\begingroup$ This gives the right result for the test case, but isn't it a bit convoluted compared with the built-in Alternatives function? $\endgroup$ – Verbeia Dec 31 '14 at 1:35
  • $\begingroup$ Yes, very much. $\endgroup$ – student_of_algeb Dec 31 '14 at 1:55

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