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Re: List concatenation - two more methods, one truly fast

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87637] Re: List concatenation - two more methods, one truly fast
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Tue, 15 Apr 2008 05:46:37 -0400 (EDT)
  • Organization: University of Bergen
  • References: <ftv8ro$7o1$1@smc.vnet.net>

carlos at colorado.edu wrote:
> 
> Observation:   timing of the first 4 methods is roughly O(n^2).
> That would suggest that Mathematica does not implement a true
>  list processor in the kernel, since building a list should be O(n).

Yes, unlike in most other languages that support a functional 
programming paradigm, expressions in Mathematica are represented as 
simple arrays in memory (and not linked lists).  This means that 
indexing is very fast, but concatenation is slow.

A linked list can be created by nesting expressions:
{1, {2, {3, {4, {5, {}}}}}}


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