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Re: select 1st column element based on criteria in 2nd column in mathematica

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124179] Re: select 1st column element based on criteria in 2nd column in mathematica
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Wed, 11 Jan 2012 17:23:02 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

You cannot directly select from a "table", as there is no such object in 
Mathematica. You want to select from a list of 2-element lists. (You may 
_display_ such a list of lists in Table form, but such a display is not 
an object upon which you'd want to operate.)

So do it like this (among other ways):

  pairs = {{1,3}, {2,4}, {3,6}, {4,1}, {5,3}, {6,2}, {7,5}, {8,2}};
  First /@ Select[pairs, Last[#] > 3 &]

The Select function pulls out those pairs that satisfy your condition; 
the condition is specified by the "pure function" that's the 2nd 
argument to Select. Finally, mapping First (First /@ ...) onto the 
result gives the first member of each pair selected.


On 1/11/12 4:18 AM, Hani wrote:
> hello, I have a question.
>
> Suppose I have a table with two columns like this:
>
> 1  3
> 2  4
> 3  6
> 4  1
> 5  3
> 6  2
> 7  5
> 8  2
>
> I want to select elements of the 1st column which its corresponding 2nd
> column elements are bigger than 3. so, the result should be {2,3,7}.  How to
> implement that in mathematica? Thanx a lot
>

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305



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