How different colors to different sections of a route on leaflet map? [R Studio] - json

Question

I have a JSON file of a long route. The file contains the lat and long of of this route.
I'm trying to mark different sections of this route based on a set of criteria (which I've compiled in a dataframe). However, I'm facing to problems:
1) How do I break up this long set of lat and longs into segments? (can't do this manually because I have many route variations)
2) How do I assign a variable color to each segment?
I intend to use leaflet map (for its interactivity), but I'm open to better suggestions.

Answer 1

When working with spatial data, it helps to know spatial classes! I am assuming you know hoe to read your JSON file as a data frame into R.
Here's a reproducible example:
library(mapview)
library(sp)
### create some random data with coordinates from (data("breweries91", package = "mapview"))
set.seed(123)
dat <- data.frame(val = as.integer(rnorm(32, 10, 2)),
lon = coordinates(breweries91)[, 1],
lat = coordinates(breweries91)[, 2])
### state condition for creation of lines
cond <- c(8, 9, 10)
### loop through conditions and create a SpatialLines object for each condition
lns <- lapply(seq(cond), function(i) {
ind <- dat$val == cond[i]
sub_dat <- dat[ind, ]
coords <- cbind(sub_dat$lon, sub_dat$lat)
ln <- coords2Lines(coords, ID = as.character(cond[i]))
proj4string(ln) <- "+init=epsg:4326"
return(ln)
})
### view lines with mapview
mapview(lns[[1]], col = "darkred") +
mapview(lns[[2]], col = "forestgreen") +
mapview(lns[[3]], col = "cornflowerblue")
Essentially, what we are doing here is create a valid sp::SpatialLines object for each condition we specify. The we plot those using mapview given you mentioned interactivity. Plotting of spatial objects can be achieved in many ways (base, lattice, ggplot2, leaflet, ...) so there's many options to choose. Have a look at sp Gallery for a nice tutorial.
Note: This answer is only valid for non-projected geographic coordinates (i.e. latitude/longitude)!