Re: Mapping tag-value lists to a third

• To: mathgroup at smc.vnet.net
• Subject: [mg132447] Re: Mapping tag-value lists to a third
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Tue, 18 Mar 2014 01:28:44 -0400 (EDT)
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```On 3/17/14 at 2:27 AM, carlos.felippa%colorado.edu at gtempaccount.com
wrote:

>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}

Pick does this, i.e.

In[1]:= tag = {0, 1, 0, 0, 0, 1, 0, 1}; val = {f1, f2, f3, f4,
f5, f6,
f7, f8};

In[2]:= tagval = Pick[val, tag, 1]

Out[2]= {f2,f6,f8}

Or could use Cases as follows:

In[3]:= Cases[Transpose[{tag, val}], {1, _}][[All, -1]]

Out[3]= {f2,f6,f8}

Not sure how timing will be for either of these with really long lists

```

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