Re: Ranks for an array of triplets
- To: mathgroup at smc.vnet.net
- Subject: [mg87551] Re: [mg87498] Ranks for an array of triplets
- From: Carl Woll <carlw at wolfram.com>
- Date: Sat, 12 Apr 2008 07:03:38 -0400 (EDT)
- References: <200804110957.FAA08413@smc.vnet.net>
Claus wrote:
>I can create an array with x,y,z triplets. x,y are on a regularly spaced
>raster, z is a RandomReal.
>For sorting the array according to the z values, I found two options,
>the second of which is significantly faster.
>However, my goal is not to sort, but to calculate the rank of the z
>value within the triplet.
>For example:
>original array Ar: {0,0,9.8},{0,1,2.3},{1,1,12.6}
>convert to: {0,0,2},{0,1,1},{1,1,3}
>
>
Ar[[All,3]] = Ordering@Ordering[Ar[[All,3]]]
will do this, as long as all the z-values are distinct.
Carl Woll
Wolfram Research
>â?? 2.3 is the smallest z-value, hence it gets assigned rank 1
>
>In my case I can reach this converted array only with extra steps:
>- separating the z-values from Ar,
>- calculating the (standardized) "RanksOfAr",
>- "gluing" the triplets back together.
>
>Is there a way to to this in one step?
>
>Thanks,
>Claus
>
>Here is the mathematica code:
>-----------------------------
>
>Make up an array with (x, y) being coordinates and z being a value at
>that (x, y) location
>
>Ar = Partition[Flatten[Table[{i, j, k},
> {i, 1, 10}
> , {j, 1, 10}
> , {k, {RandomReal[]}}
> ]], 3];
>
>
>
>
>Time two versions of Sorting the array Ar according to z
>
>Timing[SortBottomAATriples = Sort[Ar, #1[[3]] < #2[[3]] &]];
>
>sll[ll_, elem_] := ll[[Ordering[ll[[All, elem]]]]]
>Timing[OrdBotAATrip = sll[Ar, 3]];
>
>Create the Ranks of z at the original position from Ar
>
>those ranks are scaled between [0, 1]
>
>RanksOfAr = Ordering[SortBottomAATriples]/Length[SortBottomAATriples];
>
>Procedure to put it all back together
>
>x = Ar[[All, 1]];
>y = Ar[[All, 2]];
>FinalAr = Transpose[{x, y, RanksOfAr}] // N;
>
>
- References:
- Ranks for an array of triplets
- From: Claus <clausenator@gmail.com>
- Ranks for an array of triplets