[R] returning quartiles of a list?

[Greg Trafton]

>>>>> Thomas Lumley writes:

>> Hi, all.  I have a list:
>> 
>> process <- c( 5 , 7 , 4 , 1 , 4 , 1)
>> 
>> and I'd like to get each half (or each third or each quartile) of
>> the list:
>> 

> n<-length(process)
> process[1:(n/2)]
> process[(n/2):1]
> process[(n/4):(n/2)]
> etc, etc,

Hmmm...  I tried this first and it only works for even lists

> process <- c( 5 , 7 , 4 , 1 , 4 , 1)
> n<-length(process)
> n
[1] 6
> process[1:(n/2)]
[1] 5 7 4

(works fine)

> process[(n/2):1]
[1] 4 7 5

(this is just a reverse of the previous)

> process[(n/2):n]
[1] 4 1 4 1

(this double counts the first 4, of course)

> process[((n/2)+1):n]
[1] 1 4 1

(but this works for even lists)

> process[(n/4):(n/2)]
[1] 5 7

(works)

> process <- c( 5 , 7 , 4 , 1 , 4 , 1, 8)

(and this is now an odd list)

> process[1:(n/2)]
[1] 5 7 4

(works fine)

> process[((n/2)+1):n]
[1] 1 4 1

(but the bit that worked for the even lists above doesn't work here
(and I don't quite understand why not...)

thanks!
greg
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