[R] Fast ave for sorted data?
zhou.zfang at gmail.com
Sun Feb 15 18:46:10 CET 2009
This is probably really obvious, by I can't seem to find anything on it.
Is there a fast version of ave for when the data is already sorted in
terms of the factor, or if the breaks are already known?
Basically, I have:
X = 0.1, 0.2, 0.32, 0.32, 0.4, 0.56, 0.56, 0.7...
Y = 223, 434, 343, 544, 231.... etc
of the same, admittedly large length.
Now note that some of the values of X are repeated. What I want to do
is, for those X that are repeated, take the corresponding values of Y
and change them to the average for that particular X.
So, ave(Y,X) will work. But it's very slow, and certainly not suited to
my problem, where Y changes and X stays the same and I need to
repeatedly recalculate the averaging of Y. Ave also does not take take
advantage of the sorting of the data.
So, is there an alternative? (Presumeably avoiding loops.)
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