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>*Reply-to*: drmajorbob at bigfoot.com

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

**Follow-Ups**:**Re: Re: Re: problem with Pick***From:*János <janos.lobb@yale.edu>

**References**:**problem with Pick***From:*"Chris Chiasson" <chris@chiasson.name>