Re: Re: problem with Pick

• To: mathgroup at smc.vnet.net
• Subject: [mg78319] Re: [mg78209] Re: [mg78194] problem with Pick
• From: DrMajorBob <drmajorbob at bigfoot.com>
• Date: Thu, 28 Jun 2007 04:26:17 -0400 (EDT)
• References: <acbec1a40706230431p4f1db9a9i4320680dda027396@mail.gmail.com> <200706251106.HAA05048@smc.vnet.net> <6321860.1182850677359.JavaMail.root@m35>

That's entirely contrary to the documentation, which says that Pick "picks
out those ELEMENTS of list for which the corresponding ELEMENT of sel is
True."

How is a list its own ELEMENT, if English words mean anything?

Bobby

On Tue, 26 Jun 2007 03:08:14 -0500, Oyvind Tafjord <tafjord at wolfram.com>
wrote:

> Chris Chiasson wrote:
>> Step to reproduce:
>> 1. Evaluate these two inputs with a fresh kernel:
>> Pick[{a,b},z[{},{1}],{__}]
>> Pick[{a,b},{{},{1}},{__}]
>>
>> Expected results:
>> {b}
>> {b}
>>
>> Actual results:
>> {b}
>> {a,b}
>>
>> Relevant Documentation:
>> Pick[list,sel,patt] picks out those list[[i1,i2,...]] for which
>> sel[[i1,i2,...]] matches patt.
>
> In this case, sel={{},{1}}. sel[[]] matches patt, and so list[[]] is
> picked out.
>
> This behavior, in which all of list gets picked, does produce a fair
> amount
> of confusion, unfortunately. It often shows up in connection with Except:
>
> In[1]:= Pick[{a, b, c}, {1, 2, 3}, Except[2]]
> Out[1]= {a, b, c}
>
> In[2]:= Pick[{a, b, c}, {1, 2, 3}, Except[2, _Integer]]
> Out[2]= {a, c}
>
> Oyvind Tafjord
> Wolfram Research
>
>>
>> Relevant Evaluation:
>> In[3]:= MatchQ[{},{__}]
>> Out[3]= False
>>
>> In[4]:= {Internal`\$CreationID,\$Version}
>> Out[4]= {853857,6.0 for Microsoft Windows (32-bit) (April 27, 2007) }
>>
>> --
>> http://chris.chiasson.name/
>
>
>

--
DrMajorBob at bigfoot.com

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