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Re: Grouping {x,y z} data set

  • To: mathgroup at
  • Subject: [mg99626] Re: Grouping {x,y z} data set
  • From: Szabolcs Horvát <szhorvat at>
  • Date: Sat, 9 May 2009 03:31:35 -0400 (EDT)
  • References: <gu301l$ok1$>

graser wrote:
> Hi!
> I have a question for you.
> I have arbitrary data set.
> For example,
> Data={{x_1,y_1,z_1},{x_2,y_2,z_1},{x_1, y_2, z_3},........{x_n, y_m,
> z_L}}

I know that this is just an example, but be aware that symbol names are 
not allowed to contain underscores in Mathematica.

> I tried to group this data set depending on z value.
> I mean I try to select all x, y values with same z value.
> But they are not evenly distributed and they are not integer either.

Sort by z values, and then use Split.

data = RandomReal[1, {20, 3}];

Split[SortBy[data, Last],
  Quotient[Last[#1], .1] == Quotient[Last[#2], .1] &]

Here I consider two z values the same if they fall into the same 
interval when dividing the real lines into intervals of length 0.1.  You 
probably need a different "sameness" condition (possibly just plain 

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