Please ignore! Misunderstood question.

My answer treats ngrams on characters not words.

A regex should be faster, this demo in the debugger for n=3 should give you a start. 

  DB<30> $str = join "", a..l

  DB<31> @res=()

  DB<32> for my $start (0..2) { pos($str) =$start; push @res, $str =~ 
+m/(.{3})/g }

  DB<33> x @res
0  'abc'
1  'def'
2  'ghi'
3  'jkl'
4  'bcd'
5  'efg'
6  'hij'
7  'cde'
8  'fgh'
9  'ijk'

[download]

NB:

(I know it's possible in a single regex without looping over start by playing around with \K or similar. I'll leave it to the regex gurus like tybalt to show it ;-)

HTH! :)

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

update

In case you want really want to include non-letters try unpack

In reply to Re: improving speed in ngrams algorithm (updated) by LanX
in thread improving speed in ngrams algorithm by IB2017

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