External sort
Borrowing from Stream_Merge here. Temporary files are automatically deleted when program is done, so no explicit clean-up required.
use File::Temp;
sub merge_streams ( @streams ) {
my @s = @streams.map({ hash( STREAM => $_, HEAD => .get ) }).grep({ .<HEAD>.defined });
return gather while @s {
my $h = @s.min: +*.<HEAD>;
take $h<HEAD>;
$h<HEAD> := $h<STREAM>.get
orelse @s .= grep( { $_ !=== $h } );
}
}
sub store (@values) {
my ($filename,$filehandle) = tempfile(:prefix('external-sort.'));
$filehandle.say: join "\n", @values.sort: +*;
$filename
}
# we're going to pretend that this is a long stream of input from stdin...
my (@chunk,@files);
for (<43 2 45 32 15 4 3 -9 45 66 0 42 78 123 -11 76 55 87 -2 64 92 34>) {
@chunk.push: $_;
@files.push: store(@chunk) and @chunk = () if @chunk.elems == 4; # limit of records per merge file
}
@files.push: store(@chunk) if @chunk;
say join ' ', merge_streams @files».&open;
Output:
-11 -9 -2 0 2 3 4 15 32 34 42 43 45 45 55 64 66 76 78 87 92 123