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Re: Counting nonzeros

• To: mathgroup at smc.vnet.net
• Subject: [mg86873] Re: Counting nonzeros
• From: Szabolcs Horvát <szhorvat at gmail.com>
• Date: Tue, 25 Mar 2008 01:13:43 -0500 (EST)
• Organization: University of Bergen
• References: <fs7iml$gma$1@smc.vnet.net>

carlos at colorado.edu wrote:
> I want to count the # of NZ entries in an arbitrary multilevel list,
> say exp, that contains only integers.  Is this the easiest way:
> 
>   k = Length[Flatten[exp]]-Count[Flatten[exp],0]

Suppose that we only have integers in the list.

Count[expr, Except[0, _Integer], Infinity]

Instead of _Integer, we could use _Symbol or _?AtomQ or some other 
pattern depending on the type of elements that need to be counted.

(_Integer was necessary to avoid counting all the compound expressions, 
such as sublists.)