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duckmap
Combined from primary sources listed below.

In Any§

See primary documentation in context for routine duckmap. 

method duckmap(&block --> Iterable) is rw is nodal
multi  duckmap(&op, \obj --> Iterable)

duckmap will apply its argument (or first argument for the sub form) to each element that behaves in such a way that the argument 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)␤»
say duckmap -> $_ where <c d e>.any { .uc }, <a b c d e f g>;
# OUTPUT: «(a b C D E f g)␤»
(('d', 'e'), 'f').duckmap(-> $_ where <e f>.any { .uc }).say;
# OUTPUT: «((d E) F)␤»
say duckmap -> $_ where <e f>.any { .uc }, (('d', 'e'), 'f');
# OUTPUT: «((d E) F)␤»
{ first => ('d', 'e'), second => 'f'}.duckmap(-> $_ where <e f>.any { .uc }).say;
# OUTPUT: «{first => (d E), second => F}␤»
say duckmap -> $_ where <e f>.any { .uc }, { first => ('d', 'e'), second => 'f'};
# 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]␤»
say duckmap *², [[1,2,3],[[4,5],6,7]];   # 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]]␤»
say duckmap -> Rat $_ { $_²}, [[1,2,3],[[4,5],6.1,7.2]];
# 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.