Re: Counting list elements above/below a given value
- To: mathgroup at smc.vnet.net
- Subject: [mg17271] Re: Counting list elements above/below a given value
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Fri, 30 Apr 1999 02:34:50 -0400
- References: <7g0qv1$drj@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Bill
Count needs a pattern; and in this case a level specification. But pattern
matching is slower than the flattening and testing (with Select) that you
have used. Here are some timings.
data= Table[Random[],{280},{280}];
Count[data, _?(#>.5&),{2}]//Timing
{6.86 Second,39219}
Count[data, x_/;x>.5,{2}]//Timing
{6.26 Second,39219}
Length[Select[Flatten[data], #1>.5&]]//Timing
{5.82 Second,39219}
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565
W.W. Sampson <w.sampson at umist.ac.uk> wrote in message
news:7g0qv1$drj at smc.vnet.net...
> I wish to count the number of elements within a list above
> a given value. I can do this using the following:
>
> Length[Select[Flatten[listname], value > #1&]]
>
> However, my list is a 280 x 280 matrix and consequently
> this takes a while to evaluate. My guess is that there
> must be something more efficient. I've tried:
>
> Count[listname, value > #1&]
>
> but the output given is 0, which I know to be incorrect.
>
> Any ideas appreciated.
>
> Bill
>