[R] splitting a data.frame

[Giovanni Petris]

This gives you what you want, I think (maybe up to the sign). 
However, you must be sure that each identifier occurs at most twice. 

Giovanni

> a
   V1 V2
1   A  1
2   A  7
3   B  4
4   B  5
5   C  3
6   D  3
7   D  2
8   E  5
9   F  5
10  F  6
> tapply(a$V2, a$V1, diff)
$A
[1] 6

$B
[1] 1

$C
numeric(0)

$D
[1] -1

$E
numeric(0)

$F
[1] 1

> From: "Gary Collins" <gco at eortc.be>
> Date: Tue, 22 Jan 2002 14:29:22 +0100
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> 
>  I have the following (simple!?) problem which I am unable to find a
>  relatively trivial solution to.
>  If I have a dataframe,
> 
>  A    1 
>  A    7
>  B    4
>  B    5
>  C    3
>  D    3
>  D    2
>  E    5
>  F    5
>  F    6
> 
>  I would like to create a new data.frame in the form
> 
>  ID    pt1    pt2
>  A    1    7
>  B    4    5
>  C    3    NA
>  D    3    2
>  E    5    NA
>  F    5    6
> 
>  so that for each identifier, in this example, A...F I have a column for 
>  each observation for each identifier... (with a maximum of 2 obs per 
>  identifier, if only 1 obs exist then the second obs pt2 is set to NA)
>  This is so I can find the absolute differences between the obs for each 
>  identifier, that is abs(pt1-pt2)
> 
>  ID  Diff
>  A    6
>  B    1
>  C    NA
>  D    1
>  E    NA
>  F    1
>  for which there may be another approach so as not to mess about creating 
>  a new dataframe
>  Any ideas?
>  Gary
> 
> 
> __________________________________________________
> Gary S. Collins, PhD,
> Statistics Research Fellow,
> Quality of Life Unit, 
> European Organisation for Research and Treatment of Cancer, 
> EORTC Data Center, 
> Avenue E. Mounier 83, bte. 11,
> B-1200 Brussels, Belgium.
> 
> Tel: +32 2 774 1 606
> Fax: +32 2 779 4 568
> http://www.eortc.be/home/qol/
> __________________________________________________
> 
> 
> 
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-- 

 __________________________________________________
[                                                  ]
[ Giovanni Petris                 GPetris at uark.edu ]
[ Department of Mathematical Sciences              ]
[ University of Arkansas - Fayetteville, AR 72701  ]
[ Ph: (501) 575-6324, 575-8630 (fax)               ]
[ http://definetti.uark.edu/~gpetris/              ]
[__________________________________________________]

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