R Parsing output from JSON API

Question

I want to retrieve data from IMF JSON RESTful Web Service API. I have found a dataset name and series code, so I submit a following request, usinng httr2 pacakge:

library(httr2)
library(tidyverse)
req <- request("http://dataservices.imf.org/REST/SDMX_JSON.svc/CompactData/IFS/PCPI_IX?startPeriod=2015&endPeriod=2020") %>% 
  req_perform()

As a result I get a list of 7 items.

How should I parse this output to get actual data? In the body item in the response there're no actual numbers. I've tried to use fromJSON from the jsonlite library but it gives me an error (Argument 'txt' must be a JSON string, URL or file).

library(jsonlite)
req <- request("http://dataservices.imf.org/REST/SDMX_JSON.svc/CompactData/IFS/PCPI_IX?startPeriod=2015&endPeriod=2020") %>% 
  req_perform() %>% 
  fromJSON()

ismirsehregal · Accepted Answer · 2024-12-04 11:25:51Z

2

There is no need to switch to {httr}

httr is superseded: only changes necessary to keep it on CRAN will be made. We recommend using httr2 instead.

Source: https://httr.r-lib.org/

You can use httr2::resp_body_json

library(httr2)
req <- request("http://dataservices.imf.org/REST/SDMX_JSON.svc/CompactData/IFS/PCPI_IX?startPeriod=2015&endPeriod=2020")
resp <- req |> req_perform()
parsed_body <- resp_body_json(resp, simplifyVector = TRUE)
parsed_body

Please see this related article.

Edit: For future readers: You might want to set simplifyVector = TRUE (coerce JSON arrays containing only primitives into an atomic vector) or simplifyDataFrame = TRUE (coerce JSON arrays containing only records (JSON objects) into a data.frame) in resp_body_json which is passed to the underlying jsonlite::fromJSON call.

edited Dec 4, 2024 at 11:25

answered Dec 3, 2024 at 13:50

ismirsehregal

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1 Comment

chris_chris Dec 3, 2024 at 17:20

Thanks a lot. I see merit in using httr2, but the problem is that it produces messy output - I created another topic on this here: stackoverflow.com/questions/79248608/…. Hopefully there's a way do get jsolnlite-like output using httr2

Ifeanyi Idiaye · Accepted Answer · 2024-12-03 13:18:41Z

0

You can use httr instead:

library(httr)
library(jsonlite)

res <- GET("http://dataservices.imf.org/REST/SDMX_JSON.svc/CompactData/IFS/PCPI_IX?startPeriod=2015&endPeriod=2020")

data <- content(res, as = "text", encoding = "UTF-8")

data_list <- fromJSON(data)

data_list

$CompactData
$CompactData$`@xmlns:xsi`
[1] "http://www.w3.org/2001/XMLSchema-instance"

$CompactData$`@xmlns:xsd`
[1] "http://www.w3.org/2001/XMLSchema"

$CompactData$`@xsi:schemaLocation`
[1] "http://www.SDMX.org/resources/SDMXML/schemas/v2_0/message https://registry.sdmx.org/schemas/v2_0/SDMXMessage.xsd http://dataservices.imf.org/compact/IFS http://dataservices.imf.org/compact/IFS.xsd"

$CompactData$`@xmlns`
[1] "http://www.SDMX.org/resources/SDMXML/schemas/v2_0/message"

$CompactData$Header
$CompactData$Header$ID
[1] "793c6858-2fb3-4af1-9612-637fd135ad32"

$CompactData$Header$Test
[1] "false"

$CompactData$Header$Prepared
[1] "2024-12-03T07:30:41"

$CompactData$Header$Sender
$CompactData$Header$Sender$`@id`
[1] "1C0"

$CompactData$Header$Sender$Name
$CompactData$Header$Sender$Name$`@xml:lang`
[1] "en"

$CompactData$Header$Sender$Name$`#text`
[1] "IMF"

$CompactData$Header$Sender$Contact
$CompactData$Header$Sender$Contact$URI
[1] "http://www.imf.org"

$CompactData$Header$Sender$Contact$Telephone
[1] "+ 1 (202) 623-6220"

$CompactData$Header$Receiver
$CompactData$Header$Receiver$`@id`
[1] "ZZZ"

$CompactData$Header$DataSetID
[1] "IFS"

$CompactData$DataSet
$CompactData$DataSet$`@xmlns`
[1] "http://dataservices.imf.org/compact/IFS"

edited Dec 3, 2024 at 13:18

answered Dec 3, 2024 at 12:36

Ifeanyi Idiaye

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1 Comment

chris_chris Dec 3, 2024 at 17:23

Thanks. I like the httr cause it produces nice tidy dataframe (see this topic: stackoverflow.com/questions/79248608/…), but I try to move to httr2 when possible, in case httr stops being supported. But I appreciate this nice work-around, it's realy useful!

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