Re: Selecting Many Things Rather Than Selecting One Thi ng From Many

*To*: mathgroup at smc.vnet.net*Subject*: [mg66205] Re: [mg66180] Selecting Many Things Rather Than Selecting One Thi ng From Many*From*: Gregory Lypny <gregory.lypny at videotron.ca>*Date*: Thu, 4 May 2006 05:20:11 -0400 (EDT)*References*: <7F445947D47B504E96A35290F059ECADBA844D@S4DE8PSAAMA.t-systems.com>*Sender*: owner-wri-mathgroup at wolfram.com

Thank you, Hartmut. The OR operator is intuitive and certainly does the trick for a short list of things to identify. Gregory On Wed, May 3, 2006, at 5:22 AM, Hartmut.Wolf at t-systems.com wrote: > >> -----Original Message----- >> From: Gregory Lypny [mailto:gregory.lypny at videotron.ca] To: mathgroup at smc.vnet.net >> Sent: Wednesday, May 03, 2006 8:45 AM >> To: mathgroup at smc.vnet.net >> Subject: [mg66205] [mg66180] Selecting Many Things Rather Than >> Selecting One Thing From Many >> >> Hello everyone, >> >> I've discovered another use or need for the Select function, which I >> suspect requires mapping of some sort. >> >> In my previous posts, members of this MathGroup kindly showed me how >> to apply Select to many columns of a matrix at once. For example, >> >> (Select[#1, #1 > K & ] & ) /@ Transpose[theMatrix] >> >> will pull out all values greater than K, where K is a number such as >> 100. >> >> But suppose now that K is a list of numbers, such as K={34, 876, >> 199}, and I simply want to extract or identify all of the >> rows in the >> first column of theMatrix equal to any one of those numbers. How >> would I do that? I started with >> >> Select[theMatrix, #[[1]]==any element of list K] >> >> and I imagine something similar could be applied to the Position >> function. >> >> Any hint would be much appreciated. >> >> Gregory >> > > Gregory, > > this is simple and perhaps good enough to identify the rows: > > In[6]:= M = Table[Random[Integer, {0, 9999}], {100000}, {5}]; // > Timing > Out[6]= {0.282 Second, Null} > > In[7]:= Position[M[[All, 1]], 34 | 199 | 876] // Timing > Out[7]= > {0.046 Second, {{4721}, {11778}, {17337}, {20008}, {20322}, > {20934}, {26451}, \ > {27608}, {27754}, {32699}, {34359}, {34653}, {39046}, {42495}, > {42506}, \ > {46940}, {49889}, {52322}, {54645}, {56331}, {57269}, {58562}, > {59262}, \ > {62137}, {62139}, {65675}, {68442}, {69835}, {71695}, {73574}, > {74835}, \ > {75793}, {88403}, {89449}, {93625}, {93871}, {97970}}} > > In[8]:= M[[59262]] > Out[8]= {199, 7540, 3117, 7756, 9193} > > -- > Hartmut