I'm trying to create a leaflet map which shows different movement paths for different months of the year. I.e. I've got a dataset showing multiple journeys per month and I want to display the movement paths separately for each month using the addTimeslider feature of the leaflet.extras2 package.
To do so I have been trying to adapt the code posted by SymbolixAU I found here: leaflet add multiple polylines
This code uses sf functions including st_linestring to create an object that can be supplied to a addPolylines leaflet function to show all movement paths at once.
I'm pretty sure for my purposes (showing data separately for each month) I have to use st_multilinestring, which takes a list of matrices containing the coordinates for multiple polylines per row (with one row per month) rather than a single polyline per row.
Once I have that I think I could supply that object to the addTimeslider function of leaflet.extras2 to achieve what I need. I'm quite sure of this because when I used the sf object created using sf_linestring inthe AddTimeslider feature I was able to use the time slider on the map to individual movement paths at a time.
However, I have been trying for hours and haven't been successful. Would be hugely grateful for any pointers, please and thank you.
Some example data:
#load packages
library(dplyr)
library(leaflet)
library(leaflet.extras2)
library(sf)
library(data.table)
# create the example dataset
data <- structure(list(arrival_month = structure(c(3L, 3L, 4L, 4L, 4L,
5L, 5L, 6L, 6L, 6L), .Label = c("January", "February", "March",
"April", "May", "June", "July", "August", "September", "October",
"November", "December"), class = c("ordered", "factor")), start_lat = c(33.40693,
33.64672, 33.57127, 33.42848, 33.54936, 33.53418, 33.60399, 33.49554,
33.5056, 33.61696), start_long = c(-112.0298, -111.9255, -112.049,
-112.0998, -112.0912, -112.0911, -111.9273, -111.9687, -112.0563,
-111.9866), finish_lat...4 = c(33.40687, 33.64776, 33.57125,
33.42853, 33.54893, 33.53488, 33.60401, 33.49647, 33.5056, 33.61654
), finish_lat...5 = c(-112.0343, -111.9303, -112.0481, -112.0993,
-112.0912, -112.0911, -111.931, -111.9711, -112.0541, -111.986
)), row.names = c(NA, -10L), class = c("data.table", "data.frame"
), .internal.selfref = <pointer: 0x0000026e5df41ef0>)
My attempt at the code:
# Convert the data into a list of matrices for each month
mnths <- c("May","March","April","June")
mat_list <- list()
for (i in mnths) {
month <- as.matrix(data %>% filter(arrival_month == i) %>% select(-1))
mat_list[[i]] <- month
}
# convert to an sf object
data_DT <- setDT(data)
sf <- data_DT[
, {
geometry <- sf::st_multilinestring(x = mat_list)
geometry <- sf::st_sfc(geometry)
geometry <- sf::st_sf(geometry = geometry)
}
, by = arrival_month
]
sf <- sf::st_as_sf(sf)
This yields the following result:
It's not correct because each row contains the coordinates for all the months, rather than just for the month in the respective row. I'm at a loss as to where to go from here - any help would be hugely appreciated.
Thanks
