Re: Re: Using Select with arrays? (Relative newbie)

*To*: mathgroup at smc.vnet.net*Subject*: [mg54306] Re: [mg54258] Re: Using Select with arrays? (Relative newbie)*From*: DrBob <drbob at bigfoot.com>*Date*: Wed, 16 Feb 2005 14:36:45 -0500 (EST)*References*: <200502140317.WAA14058@smc.vnet.net> <200502150250.VAA27328@smc.vnet.net> <opsl80wafhiz9bcq@monster.ma.dl.cox.net> <873831F5-D563-4249-AE56-DB483366BFDF@yale.edu>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

That works, but you're not using the Listable attribute of Max; in fact, Max isn't Listable. Attributes@Max {Flat,NumericFunction,OneIdentity,Orderless,Protected} But my solution is actually bogus, in case the Max overall for the second coordinate isn't found in the subset that has 1 in the first coordinate. A more general solution is: Last@Sort@Cases[data,{1,_,_,_,_}] {1,4,string4,c,d} That requires the two positions used to be first and second, as they are in this case. If we wanted 1 in the second position and maximum in the first position, it's simple again: Last@Sort@Cases[data,{_,1,_,_,_}] {4,1,string2,c,d} But if the key positions are 2nd and 4th, for instance, it's more complicated. For instance: data=RandomArray[BinomialDistribution[20,.1],{25,5}] #[[Ordering[#[[All,4]],-1]]]&@Cases[data,{_,1,_,_,_}] {{1,1,1,1,2},{3,2,2,0,5},{0,2,6,2,2},{3,2,3,4,3},{5,1,3,1,3},{2,2,3,1,2},{ 1,2,1,1,2},{1,1,1,3,0},{1,2,3,5,2},{2,2,2,1,3},{3,3,1,2,2},{1,0,2,1,1},{ 2,1,1,4,2},{2,3,2,2,1},{2,0,0,1,6},{1,3,2,4,2},{3,0,4,2,2},{1,0,0,0,2},{ 3,1,0,1,3},{3,4,1,1,1},{2,2,4,1,3},{1,4,1,2,2},{3,1,2,1,3},{1,2,0,2,2},{ 0,1,0,1,1}} {{2,1,1,4,2}} Max@data[[All,4]] 5 That's still reasonably simple, I think. Bobby On Tue, 15 Feb 2005 13:50:05 -0500, János <janos.lobb at yale.edu> wrote: > Bobby, > > Elegant and fast. I added to my "pearls collection" of mathgroup > contributions. > > I see that I could have used the Listable attribute of Max. So, here > is a shorter version, still just with Select. > > In[25]:= > Select[data, > #1[[2]] == Max[data[[All, > 2]]] && #1[[1]] == > 1 & ] > Out[25]= > {{1, 4, string4, c, d}} > > Thanks a lot, > > János > P.S. Here is another way with Pick and Map --not as elegant. > > In[52]:= > Pick[data, > (#1[[2]] == Max[data[[All, > 2]]] && #1[[1]] == > 1 & ) /@ data] > Out[52]= > {{1, 4, string4, c, d}} > > On Feb 15, 2005, at 12:15 PM, DrBob wrote: > >> data = {{1, 1, string1, c, d}, >> {1, 2, string2, c, d}, >> {1, 3, string3, c, d}, >> {1, 4, string4, c, d}, >> {2, 1, string1, c, d}, >> {2, 2, string2, c, d}, >> {3, 1, string3, c, d}, >> {4, 1, string2, c, d}, >> {4, 2, string4, c, d}}; >> Cases[data, {1, Max[data[[All,2]]], _, _, _}] >> {{1, 4, string4, c, d}} >> Bobby >> On Mon, 14 Feb 2005 21:50:53 -0500 (EST), János <janos.lobb at yale.edu> >> wrote: >>> Well, I did not read to the end at first. >>> If you want to use Select to select the element which has maximum in >>> its #2 location from all those who have 1 in their #1 location, then >>> you can do something like: >>> In[23]:= >>> Select[Select[data, >>> #1[[1]] == 1 & ], >>> #1[[2]] == Max[ >>> Select[data, >>> #1[[1]] == 1 & ][[All, >>> 2]]] & ] >>> Out[23]= >>> {{1, 4, string4, c, d}} >>> János >>> On Feb 13, 2005, at 10:17 PM, Hugo Mallinson wrote: >>>> The subject might not be entirely correct, but here is my problem: >>>> I have a list of 5-variable data points like >>>> data = { >>>> {1, 1, string1, c, d} >>>> {1, 2, string2, c, d} >>>> {1, 3, string3, c, d} >>>> {1, 4, string4, c, d} >>>> {2, 1, string1, c, d} >>>> {2, 2, string2, c, d} >>>> {3, 1, string3, c, d} >>>> {4, 1, string2, c, d} >>>> {4, 2, string4, c, d} >>>> } >>>> and I want to extract just the points that have 1 (or 2, etc) as >>>> their >>>> first value. I think I should do something like >>>> Select[data, {1, _Integer, _String, _Integer, _Integer}] >>>> but that doesn't work. >>>> Having done that I need to find the maximum value of #2 for each >>>> string, which I presumably do by the same method as above to extract >>>> all string1 (or ...2) and then use Map[] and Max[]. I would do this >>>> all >>>> with For loops (revealing my lack of Mathematica chops :-) ) but I'd >>>> really like to learn how to do this sort of extraction in a >>>> Mathematica-y way. Any help would be greatly appreciated! >>>> Hugo >>> ---------------------------------------------- >>> Trying to argue with a politician is like lifting up the head of a >>> corpse. >>> (S. Lem: His Master Voice) >> -- >> DrBob at bigfoot.com >> www.eclecticdreams.net > > > > -- DrBob at bigfoot.com www.eclecticdreams.net

**References**:**Using Select with arrays? (Relative newbie)***From:*Hugo Mallinson <hfm21@cam.ac.uk>

**Re: Using Select with arrays? (Relative newbie)***From:*János <janos.lobb@yale.edu>