Re: Mapping tag-value lists to a third
- To: mathgroup at smc.vnet.net
- Subject: [mg132467] Re: Mapping tag-value lists to a third
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Sun, 23 Mar 2014 05:00:18 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- Delivered-to: l-mathgroup@wolfram.com
- Delivered-to: mathgroup-outx@smc.vnet.net
- Delivered-to: mathgroup-newsendx@smc.vnet.net
On 3/22/14 at 12:06 AM, koopman at 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)