[R] apply regression to an array

[Adrienne Wootten]

R-Helpers,

I've seen some similar threads about this question online, but not quite
what I'm looking for.  I apologize in advance if someone's already answered
this and I just can't find it online.

Say that I have an array like test3 in the little example code I have below:

test1 = array(rep(1:10,each = 25),dim=c(5,5,10))
test2 = array(rnorm(250,0,0.35),dim=c(5,5,10))
test3 = test1+test2 # array with 5 rows, 5 columns, 10 slices

time=1:10

Where the dimensions are x, y, and time.  What I'd like to do is run a
regression (for the sake of this example, say lm) on each x,y in time.  So
for a single cell the formula might be test3[1,1,]~time, but I'd like to
that for all cells.  The only way I can immediately think of is to use a
loop, but I'm wondering if there's a way to do this without a loop.
Perhaps with tapply?

I'm actually doing a fourth order regression with a much larger array, but
this simple example illustrates the question I have.

Many thanks for the help! Sorry if someone's already answered this and I
can't find it.

Adrienne

-- 
Adrienne Wootten
Graduate Research Assistant
State Climate Office of North Carolina
Department of Marine, Earth and Atmospheric Sciences
North Carolina State University

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