我想从 comtrade 数据库的 API 调用中创建一个数据框。comtrade 数据库本身就提供了此代码。但是，为我的参数修改它不会产生预期的输出。
代码如下所示：
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$validation, recursive = TRUE)
ndata <- NULL
if (length(data) > 0) {
var.names <- names(data[[1]])
data <- as.data.frame(t(sapply(data,rbind)))
ndata <- NULL
for (i in 1:ncol(data)) {
data[sapply(data[,i],is.null),i] <- NA
ndata <- cbind(ndata, unlist(data[,i]))
}
ndata <- as.data.frame(ndata)
colnames(ndata) <- var.names
}
return(list(validation = validation,data = ndata))
}
}
}
但是，执行代码会导致两个错误：
reporters <- fromJSON(file=string)
Error in readLines(file, warn = FALSE) : 'con' is not a connection
reporters <- as.data.frame(t(sapply(reporters$results,rbind)))
Error in reporters$results : object of type 'closure' is not subsettable
和字符串包含以下信息：
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
任何类型的帮助推荐并以良好的业力为荣，
最好的问候，萨拉