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MathGroup Archive 2005

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54304] Re: [mg54258] Re: Using Select with arrays? (Relative newbie)
  • From: János <janos.lobb at yale.edu>
  • Date: Wed, 16 Feb 2005 14:36:37 -0500 (EST)
  • References: <200502140317.WAA14058@smc.vnet.net> <200502150250.VAA27328@smc.vnet.net> <opsl80wafhiz9bcq@monster.ma.dl.cox.net>
  • Sender: owner-wri-mathgroup at wolfram.com

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


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