On Wed, 3 Mar 2010, Worik R wrote:
I have a zoo object z
z
Value
2003-11-15 2.22
2003-11-17 2.26
2003-11-19 2.28
2003-11-22 2.54
2003-11-26 2.55
I wish to find the entry 2 entries before "2003-11-26". How do I do this?
If you want to find out that this is at the third position you can ask
which(time(z) == "2003-11-26") - 2
and the whole observation could be extracted via
z[which(time(z) == "2003-11-26") - 2, ]
If you want to query just the data value you could also use lag(), e.g.
window(lag(z, -2), as.Date("2003-11-26"))
hth,
Z
I thought I might be able to say index(z["2003-11-26"]) and have it return 5
so I could then say z[3]. But this does not work.
I can not find an answer in ?index
In the meantime I am using a loop, can any one help?
cheers
Worik
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