Wolfram: Scan (foreach)

Map but return Null (aka Foreach)

Scan[f, list]

Same as Map, but return Null. [see Wolfram: Map Function to List]

Scan allows the use of Return and Throw to exit and return a alternative value.

• Scan

xx = {a, {{b,c}, d}, e};

(* map to leafs, but as soon as c is found, exit. *)

Scan[
 Function[{x},
  Print[ x ];
   If[x === c, Return[x] ]],
 xx,
 {-1} ]

(* 
a
b
c
Null
 *)

🟢 tip: When to Use Scan

Scan is useful when:

• You want to go over every element, but do not need the return value. In JavaScript known as “foreach”. [see JS: Array.prototype.forEach]
• You want to go over every element, but as soon as a condition is found, exit.
• Scan allows you to map a function to leafs of a tree or other levels of nodes, using levelspec (like Map), but as soon as a condition is found, exit.