On Jan 13, 2009, at 10:28 AM, Gabor Grothendieck wrote:
If efficiency is not of concern then this is easy to understand:
for(i in 1:5) for(j in 1:5) if (i < j) { ... }
or?:
> xx <- expand.grid(i=1:5, j=1:5)
> subset(xx, i < j)
i j
6 1 2
11 1 3
12 2 3
16 1 4
17 2 4
18 3 4
21 1 5
22 2 5
23 3 5
24 4 5
--
David Winsemius
On Tue, Jan 13, 2009 at 8:20 AM, Niccolò Bassani
<biostatist...@gmail.com> wrote:
Dear R users,I come to you with a quite silly question I think, but
I hope
you can answer me...
That is, I've got some problems in using the if and while
conditions in a
loop.
Substantially, I want to select rows in a dataset depending on an
index
variable (suppose it ranges from 1 to 5), so to make a specific
analysis
(homemade of course) on thie new dataset. Mi first tought has been
to do a
double loop like this:
for i in 1:5{
for j in (i+1):5{
data = dataset[(variable==i) | (variable==j),]
##analysis
##analysis
}
}
This way I should select all the couples only once (gaining in
efficiency I
hope). The fact is that this arrangement has a problem: that j ends
up with
ranging from 2 to 6, not from to 2 to 5. So when I do a subsetting
on the
dataset to obtain only the rows corresponding to the values of i
and j I
want, when the loop comes to j = 6 I have an error, of course.
What I want to know is: how can I use the if or while condition in
such a
loop to avoid the routine doing the computations for this case?
I.e., can I
tell somehow R "Hey, if j=6, let it go and move on with the other
computations"?
Or maybe you can see a faster and better way of using the for
conditions??
I hope I made myself clear, if not I'll carify myself!!
Thanks in advance
Niccolò
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