catchment_areas

pkgs <- c('data.table', 'httr', 'jsonlite')
lapply(pkgs, require, char = TRUE)

get_catch_postcodes <- function(x_lon, y_lat, tm = 120){  
    # <tm> input travel time is in minutes
    # output travel time is in seconds
    # output travel distance is in metres
    appId  <- 'INSERT HERE YOUR ID'
    apiKey <- 'INSERT HERE YOUR API KEY'
    requestBody <- paste0('{ 
        "arrival_searches" : [{
            "id" : "catchment areas", 
            "coords": {"lat":', y_lat, ', "lng":', x_lon,' }, 
            "transportation" : {"type" : "driving"} ,
            "arrival_time" : "2018-09-20T19:00:00Z",
            "travel_time" : ', tm * 60, ',
            "properties": ["travel_time", "distance"]
        }] 
    }')
    y <- POST(
        url = "http://api.traveltimeapp.com/v4/time-filter/postcodes",
        add_headers('Content-Type' = 'application/json'),
        add_headers('Accept' = 'application/json'),
        add_headers('X-Application-Id' = appId),
        add_headers('X-Api-Key' = apiKey),
        body = requestBody,
        encode = "json"
    )
    y <- fromJSON(as.character(y))    
    y1 <- unlist(y$results$postcodes[[1]]$properties)
    y <- data.table(
            'postcode' = y$results$postcodes[[1]]$code,
            'time' = y1[names(y1) == 'travel_time'],
            'distance' = y1[names(y1) == 'distance']
    )
    y[order(time, distance)]
}

# load data 
places <- read_fst(file.path(path, 'places'), as.data.table = TRUE)
postcodes <- read_fst(file.path(geo_path, 'postcodes'), columns = c('postcode', 'OA'), as.data.table = TRUE)

# download driving data
dts <- NULL
for(idx in 1:nrow(places)){
    message('Calculating values for ', places[idx, name], ' with id ', places[idx, place_id])
    y <- get_catch_postcodes(places[idx, x_lon], places[idx, y_lat])
    dts <- rbindlist(list( dts, data.table('place_id' = places[idx, place_id], y) ))
    Sys.sleep(2)
}

# normalize postcode
dts[nchar(postcode) == 8, postcode := gsub(' ', '', postcode)]
dts[nchar(postcode) == 6, postcode := gsub(' ', '  ', postcode)]

# add OA
dts <- postcodes[dts, on = 'postcode']
dts <- dts[!is.na(OA)]

# add time class 
max_time <- max(dts$time)/60
dtime <- 15
dts[, ctime := cut(
    time / 60, 
    seq(0, max_time, dtime), 
    paste0('(', seq(0, max_time - dtime, dtime), '-', seq(dtime, max_time, dtime), ']'),
    ordered = TRUE
)]

# add distance class
max_dist <- ceiling(max(dts$distance/10000, na.rm = TRUE)) * 10
cuts <- c(0, 2, 5, 10, 25, seq(50, max_dist, 50))
if(max_dist > cuts[length(cuts)]) cuts <- c(cuts, cuts[length(cuts)] + 50)
dts[, cdistance := cut(
    distance / 1000, 
    cuts, 
    sapply(2:length(cuts), function(x) paste0('(', cuts[x-1], '-', cuts[x], ']')),
    ordered = TRUE
)]