R - get weather data from openweather api

Table of Contents

• 1. get weather data an from openweather via R

1 get weather data an from openweather via R

• load the rjson package which is able to parse json into R formats
  
• set the file argument to the uri
  
• within the uri you can specify the city or a weather station (see http://openweathermap.org/api for details), here are a example by station
  

require(rjson)
tt <- fromJSON(file=
  "http://api.openweathermap.org/data/2.5/history/station?id=7447&type=day")

• the fromJSON() command converts the JSON formatted data into a list
  
• the list element named list contains the weather data for one month previous in the free account
  
• the little function extract.temp() below, extracts the min and max temperature and the wind speed (together with the time)
  

extract.temp <- function(x){
    return(data.frame(min=x$temp$mi-273.15,
                      max=x$temp$ma-273.15,
                      wind=unlist(x$wind$speed[1]),
                      tstmp=x$dt))
}

temps <- Reduce(rbind,lapply(tt$list , extract.temp))
temps$tstmp <- as.Date(as.POSIXct(temps$tstmp,
                       origin = as.Date("1970-01-01")))
head(temps)

   min max wind      tstmp
v   16  26 1.42 2014-10-05
v1  12  23 2.31 2014-10-06
v2  14  24 2.12 2014-10-07
v3  15  25 3.14 2014-10-08
v4  15  25 3.33 2014-10-09
v5  16  25 3.14 2014-10-10

• now we plot the data using the symbols() command, plotting wind speed on the y-axis and time on the x-axis (there is some mix-up because of the the beginning of winter time (from daylight saving time) on oct, 26th
  

nod <- length(tt$list)

symbols(x=temps$tstmp,
        y=temps$wind,
        thermometers = cbind(.4,1.6,temps$min/40,temps$max/40),
        fg = "red",
        ylim = c(-0.5,max(temps$wind)+1),
        xaxt="n",
        xlab = "day", ylab="wind speed",
        main="Temperature of the last 30 days")
axis(1,at=temps$tstmp,labels=
                substr(as.character(temps$tstmp),6,10),las=2)

 text(x=temps$tstmp,
      y=temps$wind-0.5,rep(0,nod),adj=c(0.5,0))
 text(x=temps$tstmp,
      y=temps$wind+0.5,rep(40,nod),adj=c(0.5,0))
 text(x=temps$tstmp,
      y=temps$wind,rep(20,nod),adj=c(0.5,0.5))

• with the little function below you can find the station ids by lat and lon
  

get.station <- function(lat,lon){
    tmpdat <- fromJSON(file=
     paste0("http://api.openweathermap.org/data/2.5/station/find?lat=",lat,
            "&lon=",lon,"&cnt=1"))
    print(paste("found:",tmpdat[[1]]$station$name,", id:",tmpdat[[1]]$station$id))
    tmpdat[[1]]$station$id
}

station <- get.station(lat=34,lon=118.3)
station

[1] "found: ZSNJ , id: 7447"
[1] 7447

get.station(51.5,0.1)

[1] "found: EGLC , id: 5091"
[1] 5091