Your skill will accomplishwhat the force of many cannot PerlMonks

### comment on

 Need Help??

### Non-recursive solution

For completeness, here's a solution that does not use a recursive subroutine:

sub nested_foreach(&@) { my \$code = shift; my @indices = map { 0 } @_; # First set of indices is all zeroes my @sizes = map { scalar @\$_ } @_; # Cache array sizes (optional) my \$k; do { # Determine the array elements corresponding to the current set # of indices, and pass them to the closure: \$code->( map { \$_[\$_][\$indices[\$_]] } 0..\$#_ ); # Determine the next set of indices: for (\$k = \$#_; \$k >= 0; \$k--) { \$indices[\$k]++; if (\$indices[\$k] < \$sizes[\$k]) { last; } else { \$indices[\$k] = 0; } } # If \$k went out-of-bounds, there are no more valid iterations: } while (\$k >= 0); } my @a = ...; my @b = ...; my @c = ...; nested_foreach { say join ' ', @_ } \@a, \@b, \@c;

The "Determine the next set of indices" step may seem a little complicated at first sight, but it becomes more intuitive if you think of the @indices array as an integer number (with each element representing a digit), and imagine that we want to "increment" that "number" by 1. It's not a decimal (i.e. base-10) number, but rather one where each digit can have a different base (i.e. the sizes of the input arrays) - but that doesn't really change anything.

Incrementing the "number" by 1 works just like the integer addition (here with an addend of 1) that you were taught back in primary school: Start with the right-most digit; increment it; if it's still within the valid range of digits then you're done; if instead it went above the limit then wrap it around to zero, "carry the one", and repeat the same steps with the next digit to the left.

Update:

### Performance comparison

Interestingly, my iterative solution seems to be significantly slower than BrowserUK's recursive solution, at least when running on my PC and with various different numbers/sizes of input arrays I tried:

sub nested_foreach(&@) { ... # see above } sub nForX(&@) { ... # see BrowserUK's post } # my @size = (500, 900); # my @size = (5, 5, 5, 5, 5, 5, 5, 5); my @size = (100, 4, 75, 23); my @AoA = map { [map { chr(\$_+64) x int(rand(10)) } 1 .. \$_] } @size; cmpthese -10, { iterative => sub { nested_foreach { join("", @_) } @AoA }, recursive => sub { nForX { join("", @_) } scalar @AoA, @AoA }, };
s/iter iterative recursive iterative 1.86 -- -71% recursive 0.532 249% --

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or or How to display code and escape characters are good places to start.

Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others making s'mores by the fire in the courtyard of the Monastery: (6)
As of 2022-05-23 12:09 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?
Do you prefer to work remotely?

Results (82 votes). Check out past polls.

Notices?