Gareth Campbell wrote:
Hello,
I have a matrix and I want to sample 20 rows that are the the percentiles of
0-100 in 0.05 increments. I have a vector of my sequence
(0, 0.05, 0.10, 0.15,....1.0) and also
That's actually 21 entries, but that probabl doesn't matter...
a normalised vector of rownumbers. That is, there are 234 rows (for
example) so I do
perc<-c(1:234/234)
which looks like a bunch of numbers from 0 - 1.
In Excel (which I try not to use at every possible occaison) you can use a
VLOOKUP function to say choose the rows from the perc vector that are the
closest match to the sequence vector - i.e. you can specify to choose the
"closest" match, it doesn't have to be an exact match.
In R, I'd normally use the grep command when I know it's an exact match.
Does anyone know how to achieve this in R?
You could do it with approx. That is:
rownum <- approxfun( (1:234 - 0.5)/234, 1:234, method="constant", rule=2)
Then rownum(0.05) will give 12, rownum(0.1) will give 23, etc.
Duncan Murdoch
Also, I've been getting heaps of help from everyone on this mailing list -
if I reply to the respondent and R Help again, will it show up in the
correct thread? I haven't been able to say thankyou as I wasn't sure it
would show up in the thread.
Thanks
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