Yes, that's faster. But it doesn't work (consider not removing elements when $index=0). When I fixed youre code, it became slower -- though it may be possible to optimize it again: 
# the fix:
@items = grep {
    my $keep = !exists $del{$_};
    $i++;
    $index -= ($i < $index) unless $keep;
    $keep
  } @items;

# the results
Benchmark: timing 100000 iterations of BrowserUk, dpuu...
 BrowserUk: 13 wallclock secs (13.72 usr +  0.00 sys = 13.72 CPU) @ 72
+88.63/s (n=100000)
      dpuu: 10 wallclock secs ( 9.88 usr +  0.00 sys =  9.88 CPU) @ 10
+117.36/s (n=100000)
             Rate BrowserUk      dpuu
dpuu      10117/s       39%        --
BrowserUk  7289/s        --      -28%

[download]
To provide fair comparison, here are the results I got running your original benchmark on my system (note the increased iteration count -- my system is 5X faster): 
Benchmark: timing 100000 iterations of BrowserUk, dpuu...
 BrowserUk: 10 wallclock secs ( 9.26 usr +  0.00 sys =  9.26 CPU) @ 10
+795.64/s (n=100000)
      dpuu: 10 wallclock secs ( 9.87 usr +  0.01 sys =  9.88 CPU) @ 10
+118.39/s (n=100000)
             Rate      dpuu BrowserUk
dpuu      10118/s        --       -6%
BrowserUk 10796/s        7%        --

[download]
in constrast to your +25/-20%. --Dave

Update: The required optimization is this twisted expression: 

@items = grep { ++$i && !exists $del{$_} || ($index -= $i-1 <= $index)
+ && 0 } @items;

[download]

In reply to Re: Re: round-robin on varying sequence by dpuu
in thread round-robin on varying sequence by dpuu

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