shiny return data based on click - r

Question

I have a global database of grid ID, lat and long at 100-km resolution and associated
data for each 100-km grid. Something like this
grid_ID Lat Lon data1 data2 data3 ... data4
I want to develop a shiny app that allows the user to:
click anywhere on the map
return corresponding lat and lon
based on the returned lat and lon, find which 100-km grid does it fall into
show the data associated with that 100-km grid as a pop-up window or as a table (either will do)
library(shiny)
library(leaflet)
library(shinythemes)
ui <- fluidPage(theme = shinytheme('superhero'),
leafletOutput("map"),
verbatimTextOutput("out")
)
server <- function(input, output, session) {
output$map <- renderLeaflet({
leaflet() %>% addProviderTiles('Esri.WorldImagery')
})
output$out <- renderPrint({
validate(need(input$map_click, FALSE))
str(input$map_click)
})
}
shinyApp(ui, server)
This is now returning lat and long of the location that I clicked on which is my
step 1 and 2. How do I go about doing step 3 and 4. For step 3, usually if it was not an shiny app, I would do
coordinates(dat) <- ~ Longitude + Latitude
proj4string(dat) <- "+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0"
GRID <- over(dat, grid_shp)
where grid_shp is my global 100-km grid shapefile and dat has the returned lat lon from the click.

Answer 1

Probably not the most elegant solution and also not sure if it's in leaflet for R, but you could define each grid rectangle as a polygon, loop through the polygons and do if(Polygon.getBounds().contains(LatLng) == true); then you know which grid square you're in. Then return the feature properties of the grid square aka polygon object.

Answer 2

I assume your dataset is called "data". You have to find the grid which intersects with the coordinates of the click.
library(shiny)
library(leaflet)
library(shinythemes)
ui <- fluidPage(theme = shinytheme('superhero'),
leafletOutput("map"),
verbatimTextOutput("out"))
server <- function(input, output, session) {
output$map <- renderLeaflet({
leaflet() %>% addProviderTiles('Esri.WorldImagery')
})
output$out <- renderPrint({
validate(need(input$map_click, FALSE))
str(input$map_click)
# create a dataframe from the clicked point
xy <-
data.frame(longitude = input$map_click$lng,
latitude = input$map_click$lat)
# transform this dataframe to spatialpointsdataframe
spdf <-
SpatialPointsDataFrame(
coords = xy,
data = xy,
proj4string = CRS("+proj=longlat +datum=WGS84 +no_defs")
)
# find the grid that intersects with the point
selected_raster <- spdf %over% data
# here you will see the information you need
as.data.frame(selected_raster)
})
}
shinyApp(ui, server)