[R] splitting a data.frame

[Gary Collins]

 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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