[R] [:]

[Chuck Cleland]

Alexy Khrabrov wrote:
> What are idioms for taking a head or a tail of a vector, either up to  
> an index, or from an index to the end?  Also -- is it necessary to  
> use length(v) to refer to the last element? E.g., Python has
> 
> v[:3] # indices 0,1,2
> v[3:] # indices 3,4,...
> v[-1] # the last element of v
> v[:-1] # all but last

?head

  For example:

> x <- runif(10)

> x
 [1] 0.60253459 0.51895186 0.01080359 0.68675829
 [5] 0.58588120 0.41019752 0.25345482 0.84928989
 [9] 0.78826981 0.01696331

> head(x, 3)
[1] 0.60253459 0.51895186 0.01080359

> tail(x, -3)
[1] 0.68675829 0.58588120 0.41019752 0.25345482
[5] 0.84928989 0.78826981 0.01696331

> tail(x, 1)
[1] 0.01696331

> head(x, -1)
[1] 0.60253459 0.51895186 0.01080359 0.68675829
[5] 0.58588120 0.41019752 0.25345482 0.84928989
[9] 0.78826981

> Cheers,
> Alexy
> 
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-- 
Chuck Cleland, Ph.D.
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