[R] help with json data from the web into data frame in R

Tue May 8 18:03:41 CEST 2018

That said, I have two issues to ask for help with:

1) how to ignore cert errors with a fromJSON call

And 

2) why the json data from the example link doesn't convert to a data frame.  As seen in the following example

library("rjson")
result <- fromJSON(file = "https://www.semantic-mediawiki.org/w/api.php?action=ask&query=[[Category:City]]|?Capital%20of|?Has%20area&format=json")
json_data_frame <- as.data.frame(result)
print(json_data_frame)

which results in:

> library("rjson")

Warning message:
package ‘rjson’ was built under R version 3.4.4 

> result <- fromJSON(file = "https://www.semantic-mediawiki.org/w/api.php?action=ask&query=[[Category:City]]|?Capital%20of|?Has%20area&format=json")
> json_data_frame <- as.data.frame(result)

Error in (function (..., row.names = NULL, check.rows = FALSE, check.names = TRUE,  : 
  arguments imply differing number of rows: 0, 1

> print(json_data_frame)

Error in print(json_data_frame) : object 'json_data_frame' not found

> 

-----Original Message-----
From: R-help [mailto:r-help-bounces using r-project.org] On Behalf Of Evans, Richard K. (GRC-H000)
Sent: Tuesday, May 08, 2018 11:52 AM
To: David Winsemius
Cc: r-help using r-project.org
Subject: Re: [R] help with json data from the web into data frame in R

Right. I'm trying to access a server within my organization which has a cert error that I cannot fix. 

The example link I provided was to a site on the web that does not have the cert error.

From the linux shell I use the "-k" switch with cURL to ignore cert errors.. is there an equivalent in the R world?

-Rich

-----Original Message-----
From: David Winsemius [mailto:dwinsemius using comcast.net] 
Sent: Tuesday, May 08, 2018 11:48 AM
To: Evans, Richard K. (GRC-H000)
Cc: Eric Berger; r-help using r-project.org
Subject: Re: [R] help with json data from the web into data frame in R

> On May 8, 2018, at 8:36 AM, Evans, Richard K. (GRC-H000) <richard.k.evans using nasa.gov> wrote:
> 
> I’ve been tinkering and discovered that the link I need to read json data from is ‘https’ and there is a certificate warning that I have to click through from a browser. That might be my issue. Is there any way in the json package to tell it to ignore self-signed cert errors in a url?

I didn't have that issue when using the link you offered:

library(jsonlite)
myJSON <- fromJSON( url("https://www.semantic-mediawiki.org/w/api.php?action=ask&query=%5B%5BCategory:City%5D%5D&format=json") )

# results in a complex list (not trivially reducible to a dataframe:

str(myJSON)
List of 1
 $ query:List of 5
  ..$ printrequests:'data.frame':	1 obs. of  5 variables:
  .. ..$ label : chr ""
  .. ..$ key   : chr ""
  .. ..$ redi  : chr ""
  .. ..$ typeid: chr "_wpg"
  .. ..$ mode  : int 2
  ..$ results      :List of 39
  .. ..$ File:2166320938 5cfc9ec72a z.jpg                      :List of 6
  .. .. ..$ printouts   : list()
  .. .. ..$ fulltext    : chr "File:2166320938 5cfc9ec72a z.jpg"
  .. .. ..$ fullurl     : chr "https://www.semantic-mediawiki.org/wiki/File:2166320938_5cfc9ec72a_z.jpg"
#-----trimmed-----------

David

> 
> -Rich
> 
> From: Eric Berger [mailto:ericjberger using gmail.com]
> Sent: Tuesday, May 08, 2018 11:31 AM
> To: Evans, Richard K. (GRC-H000)
> Cc: r-help using r-project.org
> Subject: Re: [R] help with json data from the web into data frame in R
> 
> Hi Rich,
> Take a look at the function fromJSON found in the rjson package.
> Note that the Usage in the help page: ?fromJSON names the second 
> argument 'file' but if you look at the description the argument can be a URL.
> 
> HTH,
> Eric
> 
> 
> On Tue, May 8, 2018 at 6:16 PM, Evans, Richard K. (GRC-H000) <richard.k.evans using nasa.gov<mailto:richard.k.evans using nasa.gov>> wrote:
> Hello
> 
> I am able to construct a url that points to some data online in the JSON format.  See an example at [0].
> 
> I would like to work with this data as a dataframe in R.
> 
> I know that there is a package for handling json data [1] but it assumes the data is in a local file but It is not clear to me how to request the data from the web in an R script and get the json data converted into a data frame in R.
> 
> Can anyone provide a basic example or some guidance please?
> 
> -Rich (revansx)
> 
> [0] 
> https://www.semantic-mediawiki.org/w/api.php?action=ask&query=[[Catego
> ry:City]]&format=json<https://www.semantic-mediawiki.org/w/api.php?act
> ion=ask&query=%5b%5bCategory:City%5d%5d&format=json>
> [1] https://www.tutorialspoint.com/r/r_json_files.htm
> 
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> 
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David Winsemius
Alameda, CA, USA

'Any technology distinguishable from magic is insufficiently advanced.'   -Gehm's Corollary to Clarke's Third Law

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