Проблемы с превращением вызова API в датафрейм

Question

Я хочу создать фрейм данных из вызова API из базы данных Comtrade. База данных Comtrade предоставляет этот код на своей стороне. Изменение его для моих параметров, однако, не дает желаемого результата.

Код выглядит так:

library("rjson")
string <- get.Comtrade(px = "HS", ps = "2002" , p = "124" , r = "842" , fmt = "json")
reporters <- fromJSON(file = string)
reporters <- as.data.frame(t(sapply(reporters$results,rbind)))

get.Comtrade <- function(url = "http://comtrade.un.org/api/get?"
                         ,maxrec = 50000
                         ,type = "C"
                         ,freq = "A"
                         ,px = "HS"
                         ,ps = "now"
                         ,r = ""
                         ,p = ""
                         ,rg = "all"
                         ,cc = "TOTAL"
                         ,fmt = "json") {
  string <- paste(
    url
    ,"max=",maxrec,"&" #maximum no. of records returned
    ,"type=",type,"&" #type of trade (c=commodities)
    ,"freq=",freq,"&" #frequency
    ,"px=",px,"&" #classification
    ,"ps=",ps,"&" #time period
    ,"r=",r,"&" #reporting area
    ,"p=",p,"&" #partner country
    ,"rg=",rg,"&" #trade flow
    ,"cc=",cc,"&" #classification code
    ,"fmt=",fmt        #Format
    ,sep = ""
  )

  if (fmt == "csv") {
    raw.data <- read.csv(string,header = TRUE)
    return(list(validation = NULL, data = raw.data))
  } else {
    if (fmt == "json") {
      raw.data <- fromJSON(file = string)
      data <- raw.data$dataset
      validation <- unlist(raw.data$validation, recursive = TRUE)
      ndata <- NULL
      if (length(data) > 0) {
        var.names <- names(data[[1]])
        data <- as.data.frame(t(sapply(data,rbind)))
        ndata <- NULL
        for (i in 1:ncol(data)) {
          data[sapply(data[,i],is.null),i] <- NA
          ndata <- cbind(ndata, unlist(data[,i]))
        }
        ndata <- as.data.frame(ndata)
        colnames(ndata) <- var.names
      }
      return(list(validation = validation,data = ndata))
    }
  }
}

Однако выполнение кода приводит к двум ошибкам:

 reporters <- fromJSON(file=string)
 Error in readLines(file, warn = FALSE) : 'con' is not a connection
 reporters <- as.data.frame(t(sapply(reporters$results,rbind)))
 Error in reporters$results : object of type 'closure' is not subsettable

и строка содержит следующую информацию:

 List of 2
 $ validation: Named chr [1:12] "Ok" "0" "0" "" ...
 ..- attr(*, "names")= chr [1:12] "status.name" "status.value"       "status.category" "status.description" ...
 $ data      :'data.frame': 3 obs. of  35 variables:
 ..$ pfCode       : Factor w/ 1 level "H2": 1 1 1
 ..$ yr           : Factor w/ 1 level "2002": 1 1 1
 ..$ period       : Factor w/ 1 level "2002": 1 1 1
 ..$ periodDesc   : Factor w/ 1 level "2002": 1 1 1
 ..$ aggrLevel    : Factor w/ 1 level "0": 1 1 1
 ..$ IsLeaf       : Factor w/ 1 level "0": 1 1 1
 ..$ rgCode       : Factor w/ 3 levels "1","2","3": 1 2 3
 ..$ rgDesc       : Factor w/ 3 levels "Export","Import",..: 2 1 3
 ..$ rtCode       : Factor w/ 1 level "842": 1 1 1
 ..$ rtTitle      : Factor w/ 1 level "USA": 1 1 1
 ..$ rt3ISO       : Factor w/ 1 level "USA": 1 1 1
 ..$ ptCode       : Factor w/ 1 level "124": 1 1 1
 ..$ ptTitle      : Factor w/ 1 level "Canada": 1 1 1
 ..$ pt3ISO       : Factor w/ 1 level "CAN": 1 1 1
 ..$ ptCode2      : Factor w/ 0 levels: NA NA NA
 ..$ ptTitle2     : Factor w/ 1 level "": 1 1 1
 ..$ pt3ISO2      : Factor w/ 1 level "": 1 1 1
 ..$ cstCode      : Factor w/ 1 level "": 1 1 1
 ..$ cstDesc      : Factor w/ 1 level "": 1 1 1
 ..$ motCode      : Factor w/ 1 level "": 1 1 1
 ..$ motDesc      : Factor w/ 1 level "": 1 1 1
 ..$ cmdCode      : Factor w/ 1 level "TOTAL": 1 1 1
 ..$ cmdDescE     : Factor w/ 1 level "ALL COMMODITIES": 1 1 1
 ..$ qtCode       : Factor w/ 1 level "1": 1 1 1
 ..$ qtDesc       : Factor w/ 1 level "No Quantity": 1 1 1
 ..$ qtAltCode    : Factor w/ 0 levels: NA NA NA
 ..$ qtAltDesc    : Factor w/ 1 level "": 1 1 1
 ..$ TradeQuantity: Factor w/ 0 levels: NA NA NA
 ..$ AltQuantity  : Factor w/ 0 levels: NA NA NA
 ..$ NetWeight    : Factor w/ 0 levels: NA NA NA
 ..$ GrossWeight  : Factor w/ 0 levels: NA NA NA
 ..$ TradeValue   : Factor w/ 3 levels "160794797453",..: 3 1 2
 ..$ CIFValue     : Factor w/ 0 levels: NA NA NA
 ..$ FOBValue     : Factor w/ 0 levels: NA NA NA
 ..$ estCode      : Factor w/ 1 level "0": 1 1 1 

Любая помощь, рекомендованная и удостоенная хорошей кармы,

С наилучшими пожеланиями, Сара

Answer 1

Я думаю, что строка должна быть назначена как:

    string <- "http://comtrade.un.org/data/cache/reporterAreas.json"

и в конце запроса функции для данных как:

    data<-get.Comtrade(px = "HS", ps = "2002" , p = "124" , r = "842" , fmt = "json")