http://beautifulcode.oreillynet.com/2008/03/four_lines_of_code_1.php
The example in the site is done in Haskell.
Following is done in J:
d=:5 10 20 4 9 8 9
f=:(3&((4%~[:+/ 1 2 1&*)\)@({.,],{:))
f^:(<5) ] d
5 10 20 4 9 8 9
6.25 11.25 13.5 9.25 7.5 8.5 8.75
7.5 10.5625 11.875 9.875 8.1875 8.3125 8.6875
8.26563 10.125 11.0469 9.95313 8.64063 8.375 8.59375
8.73047 9.89063 10.543 9.89844 8.90234 8.49609 8.53906
load 'plot'
plot f^:(<10) ] d
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