Re: problem with Pick

*To*: mathgroup at smc.vnet.net*Subject*: [mg78209] Re: [mg78194] problem with Pick*From*: Oyvind Tafjord <tafjord at wolfram.com>*Date*: Tue, 26 Jun 2007 04:08:14 -0400 (EDT)*References*: <acbec1a40706230431p4f1db9a9i4320680dda027396@mail.gmail.com> <200706251106.HAA05048@smc.vnet.net>

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/

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