determine avg hourly temperature of 3 airports via json query

pricenomics.R

library('RJSONIO')
library('plyr')

# get data
source <- "http://dl.dropbox.com/u/274/readings_formatted.json"
data_raw <- fromJSON(source)

# format data into dataframe
data <- do.call('rbind.fill', lapply(data_raw, as.data.frame))
data$timestamp <- as.POSIXlt(data$timestamp)
data$day <- as.numeric(strftime(data$timestamp, format="%d"))
data$hour <- as.numeric(strftime(data$timestamp, format="%H"))

# subset data by city
sfo <- data[ which(data$location == 'SFO'), ]
nrt <- data[ which(data$location == 'NRT'), ]
iad <- data[ which(data$location == 'IAD'), ]

# deprecated # returns a list of avg temperatures (per hour) given a city
getAverageHourlyTemp <- function(dataset){
  v = 1:24
  for (i in 1:24){
    hourset = dataset[which(dataset$hour == i-1),]
    sum = sum(hourset$temperature)
    v[i] = sum/nrow(hourset)
  }
  return(v)
}

# helper function that returns the average temperature of a city given a day and hour
getAvgFromDH <- function(dataset, day, hour){
  subset = dataset[which(dataset$hour == hour & dataset$day == day),]
  sum = sum(subset$temperature)
  return(sum/nrow(subset))
}

# function that proves result is true (verify result)
getX <- function(nrt,iad,sfo){
  a = getAvgFromDH(nrt,15,13)
  b = getAvgFromDH(iad,16,14)
  c = getAvgFromDH(sfo,17,13)

  return(floor(c^(b-a-7)))
}