sub-selecting spatial data by distance from a different point(set)

Hi Sean,

Take a look at the spDistsN1 function to calculate the distances from 
a single point to all other points. You can then make the subset based 
on the distance. What could also be an options is to build a polygon 
that has the radius around the point you are taking the distance from, 
and then use overlay to find which points are in the radius polygon. 
This might be faster when using a large dataset. I'm not sure how nto 
make the polygon, but it should be possible. But you could first take 
a look at spDistsN1.

cheers,
Paul

Sean O'Riordain wrote:

Good afternoon,

Apologies if this seems a basic question but I'm quite new to spatial
analysis (1 week now!) and I'm reading and learning as fast as I can.
I've read the Spatial Data task view, "Analysing spatial point
patterns in R" by Bradley and I've ordered "Applied Spatial Data
Analysis with R" - but it hasn't arrived yet...  I've looked and
searched - but I'm guessing that I'm not using the right buzzwords...

I have a data.frame (call it A) of about 2 million X,Y points each
with info with various characteristics, numeric and factor.  I have a
separate much smaller data.frame (call it B) of say 500 rows of X,Y
and I'd like to be able to pull a subset of A, so that for each B[i,]
I will get all rows from A that are within a given straight line
distance (i.e. within a short 'as the crow flies' radius).

Could somebody please give me some starting hints please?

Thanks in advance,
Sean O'Riordain