Documentation for method duckmap assembled from the following pages:

Class: Any §

From Any

(Any) method duckmap §

Defined as:

method duckmap(&block) is rw is nodal

duckmap will apply &block on each element that behaves in such a way that &block can be applied. If it fails, it will descend recursively if possible, or otherwise return the item without any transformation. It will act on values if the object is Associative.

<a b c d e f g>.duckmap(-> $_ where <c d e>.any { .uc }).say;
# OUTPUT: «(a b C D E f g)␤» 
(('d', 'e'), 'f').duckmap(-> $_ where <e f>.any { .uc }).say;
# OUTPUT: «((d E) F)␤» 
{ first => ('d', 'e'), second => 'f'}.duckmap(-> $_ where <e f>.any { .uc }).say;
# OUTPUT: «{first => (d E), second => F}␤» 

In the first case, it is applied to c, d and e which are the ones that meet the conditions for the block ({ .uc }) to be applied; the rest are returned as is.

In the second case, the first item is a list that does not meet the condition, so it's visited; that flat list will behave in the same way as the first one. In this case:

say [[1,2,3],[[4,5],6,7]].duckmap( *² ); # OUTPUT: «[9 9]␤»

You can square anything as long as it behaves like a number. In this case, there are two arrays with 3 elements each; these arrays will be converted into the number 3 and squared. In the next case, however

say [[1,2,3],[[4,5],6.1,7.2]].duckmap( -> Rat $_ { $_²} );
# OUTPUT: «[[1 2 3] [[4 5] 37.21 51.84]]␤»

3-item lists are not Rat, so it descends recursively, but eventually only applies the operation to those that walk (or slither, as the case may be) like a Rat.

Although on the surface (and name), duckmap might look similar to deepmap, the latter is applied recursively regardless of the type of the item.