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Scan

Scan[f, expr]
evaluates f applied to each element of expr in turn.
Scan[f, expr, levelspec]
applies f to parts of expr specified by levelspec.
  • Scan[f, expr] discards the results of applying f to the subexpressions in expr. Unlike Map, Scan does not build up a new expression to return.
  • You can use Return to exit from Scan. Return[ret] causes the final value of Scan to be ret. If no explicit return values are specified, the final result from Scan is Null.
  • Scan is useful in carrying out an operation on parts of expressions where the operation has a "side effect", such as making an assignment.
  • Scan uses standard level specifications:
nlevels 1 through n
Infinitylevels 1 through Infinity
{n}level n only
{n1,n2}levels n1 through n2
  • The default value for levelspec in Scan is {1}.
  • A positive level n consists of all parts of expr specified by n indices.
  • A negative level -n consists of all parts of expr with depth n.
  • Level -1 consists of numbers, symbols and other objects that do not have subparts.
  • Level 0 corresponds to the whole expression.
  • With the option setting Heads->True, Scan includes heads of expressions, and their parts. »
  • Scan traverses the parts of expr in a depth-first order, with leaves visited before roots.
  • If expr is a SparseArray object, Scan[f, expr] applies f only to the values or subarrays that explicitly appear in expr.
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