Gist used to create hidden answers for challenge questions in Intro to GIS in R course (https://ryan-hill.github.io/sfs-r-gis-2018/)

gages-near-portland.R

#Read in gages data and convert to spatial points data frame
#Give it the **pts** CRS and reproject to **pts2** CRS
#Select out Portland and use `gDistance` from `rgeos` package with portand as x and gages as y in the function.
#Sum across TRUE/FALSE values in query. R will count TRUE == 1 and FALSE == 0.

library(sp); library(rgeos)

gages <- read.csv('./data/StreamGages.csv')
gages <- SpatialPointsDataFrame(gages[c('LON_SITE','LAT_SITE')], gages)
gages@proj4string <- pts@proj4string
gages <- spTransform(gages, proj4string(pts2))

portland <- pts2[pts2$cities == 'Portland', ]

m <- gDistance(portland, gages, byid=T)
sum(m < 50000)

#Bonus - How to get the station names within 50km
gages$STATION_NM[which(m < 50000)]