Re: Mapping tag-value lists to a third
- To: mathgroup at smc.vnet.net
- Subject: [mg132443] Re: Mapping tag-value lists to a third
- From: Ray Koopman <koopman at sfu.ca>
- Date: Tue, 18 Mar 2014 01:27:23 -0400 (EDT)
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- Delivered-to: l-mathgroup@wolfram.com
- Delivered-to: mathgroup-outx@smc.vnet.net
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Pick[val, tag, 1]
----- carlos felippa%colorado edu <carlos.felippa%colorado.edu at gtempaccount.com> wrote:
> Hi,
>
> I have 2 lists of equal length such as
>
> tag={0, 1, 0, 0, 0, 1, 0, 1}; val={f1,f2,f3,f4,f5,f6,f7,f8}
>
> and want to produce a third:
>
> tagval={f2,f6,f8}
>
> with length Count[tag,1] containing the entries of val marked by 1-tags. Should be
> something efficient, since the source lists may be large (10^6 to 10^7). Thanks.
>