Not sure what your overall goal is here. (Won't the slopes along the coastline all be about 0?). If there are two adjacent points with different slopes from the raster, which value would you want to attach to the line segment between those points?

But you could approach the task in a different, more straightforward way:
Run the module v.split on your original coastline line vector and split to segments at whatever max distance you choose, Then run v.rast.stats with that split line as input and use your slope raster to derive slopes. The result will be an attribute table attached to the coastline vector with min,max,mean, etc raster values for each line segment.
 

On 03/06/2018 06:02 PM, thepatton...@gmail.com wrote:
I have a high-resolution vector coastline, and I extracted the vertices of this coastline to points using 'v.to.points use=vertex'. I am trying to find the nearest raster slope value from another map to these points, and then upload this slope to the attribute table of the vector points coastline. To do this, I converted the raster slope map to points with r.to.vect, and successfully uploaded the nearest slope value from the now vector slope map to the vector points coastline with v.distance, using a dmax=200.

Ok, now to my problem: I want to get the vector coastline points back onto the original vector *lines* coastline, with all the point attributes as well. Since the vector coastline points were derived from the vertices of the coastline map in the first place, they are spatially  coincident, but I can't find a processing method that does this. Ideally, I suppose the coastline points map could act as breakpoints to the coastline polyline map, and the attributes would be transferred based on a buffer of something like one metre or less. 

Any ideas on how I might do this?

Thanks,

--
Eric
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-- 
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
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