Groups > comp.soft-sys.math.mathematica > #16687

Re: Mapping tag-value lists to a third

From	Bill Rowe <readnews@sbcglobal.net>
Newsgroups	comp.soft-sys.math.mathematica
Subject	Re: Mapping tag-value lists to a third
Date	2014-03-23 09:00 +0000
Message-ID	<lgm7s9$25$1@smc.vnet.net> (permalink)
Organization	Time-Warner Telecom

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On 3/22/14 at 12:06 AM, koopman@sfu.ca (Ray Koopman) wrote:

>For v5+ users,

>val[[ SparseArray[tag] /. SparseArray[_,_,_,d_] :> Flatten@d[[2,2]]
>]]

>may be faster than Pick[val,tag,1].

For what it is worth

In[1]:= n = 10^7;
val = RandomReal[1, n];
tag = RandomInteger[1, n];

In[4]:= Timing[c = Pick[val, tag, 1];]

Out[4]= {0.137875,Null}

In[5]:= Timing[
 b = val[[SparseArray[tag] /.
      SparseArray[_, _, _, d_] :> Flatten@d[[2, 2]]]];]

Out[5]= {0.255513,Null}

In[6]:= b == c

Out[6]= True

In[7]:= $Version

Out[7]= 9.0 for Mac OS X x86 (64-bit) (January 24, 2013)

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Re: Mapping tag-value lists to a third Bill Rowe <readnews@sbcglobal.net> - 2014-03-23 09:00 +0000

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