> >
> > sub unique{ [ keys {map { $_{$_} = 1 } @_ }] }
> ^^^^^^^^^^^^^^^^^^^^^^
>
> This returns a list of the results of the block { $_{$_} = 1 }
> as evaluated for each value in @_.
>
> But the value of the expression $_{$_} = 1 is always 1, to
> your map() is returning a list of 1's. This is obviously
> not suitable for converting to a hash to pass to keys().
>
> You probably want:
>
> map { ($_ => 1) } @_;
>
> This creates a list of (key, 1) pairs for each element in @_.
> So if @_ contains 'foo','bar','baz', the map output list
> will be:
This has enligtened me somewhat as I spotted the
keys %{{map {($_ => 1)} @_}}
method after I had made the post but I was trying it doing this
[ keys %{{map { $_{$_} = 1 } @_ }}]
which as stated above is complete bollocks so thanks for the pointer. I
need to read more at perldoc -f map. Something I lack a lot in is the
different methods for record construction.
>
> 'foo', 1, 'bar', 1, 'baz', 1
>
> Now, you can create a ref to an anonymous hash out of that
> list by:
>
> {map {($_ => 1)} @_}
>
> To dereference that to a hash to pass to keys(), you would use:
>
> %{{map {($_ => 1)} @_}}
>
> Now the final sub is:
>
> sub unique { keys %{{map {($_ => 1)} @_}} }
>
> (I removed the square brackets to return a list instead of an
> array ref. Your choice.)
After I made the mods as suggested below.
sub GrepMe { [keys %{{map {($_ => 1)} @_}}] }
sub GrepMe3 { [ grep { not $\{$_}++ } @_ ] }
I benchmarked the two and the this is the results.
Checking with array Sizes 249 and 2599999
Benchmark: timing 500000 iterations of GrepMe, GrepMe3...
GrepMe: 3 wallclock secs ( 2.21 usr + 0.00 sys = 2.21 CPU) @
226039.78/s (n=500000)
GrepMe3: 2 wallclock secs ( 2.06 usr + 0.00 sys = 2.06 CPU) @
242483.03/s (n=500000)
The Functions return SAME lists
They also have the same count of elements: 12
Although the map is faster than the original unique routines the grep
is still the DB's. I suppose I should now look into the relative merits
of one above the other.
Harry
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