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.
Details and Options
- 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.
- You can also use Throw to exit from Scan. »
- 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:
-
n levels 1 through n Infinity levels 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 an Association object, Scan[f,expr] applies f only to the values in the association.
- If expr is a SparseArray object, Scan[f,expr] applies f only to the values or subarrays that explicitly appear in expr.
- Scan[f][expr] is equivalent to Scan[f,expr].