Question

我是R的初学者（仍然在编程＆＃34; R编程＆＃34; Coursera课程），我试图练习将一些简单的代码从Python移植到R. / p>

目前，我正在尝试为KairosDB database进行API调用。为了进行查询，我需要使用json.dumps()（来自json本机库）对Python对象进行编码，但我已经搜索了很多内容并且我不知道如何我可以用R和它的jsonlite库来做到这一点。我甚至不知道我是否正确地创建了JSON对象，但这是我在某些搜索中发现的。

我的代码用Python 3编写（from this repo）：

import requests
import json

kairosdb_server = "http://localhost:8080"

# Simple test
query = {
   "start_relative": {
        "value": "4",
        "unit": "years" 
   },
   "metrics": [
       {
           "name": "test",
           "limit": 10000
       }
   ]
}
response = requests.post(kairosdb_server + "/api/v1/datapoints/query", data=json.dumps(query))
print("Status code: %d" % response.status_code)
print("JSON response:")
print(response.json())

我目前使用R 3.2.3编写的代码：

library(httr)
library(jsonlite)

kairosdb_server <- 'http://localhost:8080'

query <- serializeJSON(toJSON('
  "start_relative": {
    "value": "4",
    "unit": "years"
  },
  "metrics": [
    {
      "name": "test",
      "limit": 1000
    }
  ]
'))

url <- paste(kairosdb_server, '/api/v1/datapoints/query')
response <- POST(url, body = query, encode = 'json')

print(paste("Query status code: ", response$status_code))
print(paste("JSON response: \n", content(response, type = 'application/json')))

如果我跑了，我收到以下错误：

print(paste("Query status code: ", response$status_code))
# [1] "Query status code:  400"

print(paste("JSON response: \n", content(response, type = 'application/json')))
# [1] "JSON response: \n list(\"query.metric[] must have a size of at least 1\")"

我做错了什么？

Answer 1

通常会将名为list的{{1}}传递给body，但是尝试让R在“指标”中保留数组是很棘手的。既然你已经拥有了原始Python结构的JSON，为什么不只是添加括号并将其作为字符向量传递？即

query <- '{"start_relative": {
    "value": "4",
    "unit": "years"
  },
  "metrics": [
    {
      "name": "test",
      "limit": 10000
    }
  ]}'

（然后只使用query中的POST。它等同于json.dumps()吐出的JSON：

# get rid of newlines and spaces just to show they are the same, 
# the server won't (shouldn't) care if there are newlines/spaces
cat(gsub(" \\]", "]", gsub("\\[ ", "[", gsub(" \\}", "}", gsub("\\{ ", "{", gsub("\ +", " ", gsub("\\n", "", query)))))))
{"start_relative": {"value": "4", "unit": "years"}, "metrics": [{"name": "test", "limit": 10000}]}

# python
json.dumps(query)
'{"metrics": [{"limit": 10000, "name": "test"}], "start_relative": {"unit": "years", "value": "4"}}'

如果您确实需要使用R数据结构，那么您最终将操纵toJSON的输出。

相当于Python＆＃34; json.dumps（）＆＃34;在R？

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