Over a million developers have joined DZone.

Building a JSON Webservice in R

· Big Data Zone

Learn how you can maximize big data in the cloud with Apache Hadoop. Download this eBook now. Brought to you in partnership with Hortonworks.

R is a programming language for mathematics and statistics. There are several R libraries available to support web development, including rjson and RJSONIO (note case – R library names are case sensitive). RJSONIO is based on rjson, but with modifications to improve performance working with large JSON payloads.

The example below returns the data required to render a scatter chart with a best fit line like this:

Chart in R-Studio

This requires that you’ve already set up rApache. To install RJSONIO, check http://cran.r-project.org/src/contrib/ to find the latest version, and use that filename in the following. It appears that CRAN removes the old versions- unfortunately they don’t have an easy way to just pull the latest.

wget http://cran.r-project.org/src/contrib/RJSONIO_1.0-1.tar.gz
R CMD INSTALL RJSONIO_1.0-1.tar.gz

The following code will pull JSON data from the URL, parse it, and return a linear model. This includes information for the graph, error bars, best fit line, axis intercepts, etc. For a charting package like ExtJS, the data may need to be re-formatted to render successfully, which fortunately R is quite good at.

setContentType("application/json")
 
library(RJSONIO)
library(utils)
 
cat(GET$data)
 
json <- fromJSON(URLdecode(GET$data))
fit <- lm(x ~ y)
 
cat(toJSON(fit))

Strictly speaking, this should be a POST, but this makes the example easier to read.

Some examples of this use the basicJSONHandler, like below. I found that this does not return numerics for JSON arrays, and opted not to use it.

h = basicJSONHandler()
x = fromJSON("[1, 2, 3]", h)

If you’ve read this far, you may enjoy my review of the R Cookbook.

This URL accepts and returns JSON results:

http://localhost:8081/R/fit.R?data={%22x%22:[1.5,2,7,8,15],%22y%22:[1.5,2,7,8,15]}

Results:

{ "assign" : [ 0,
      1
    ],
  "call" : { "" : "lm",
      "formula" : [ "~",
          "x",
          "y"
        ]
    },
  "coefficients" : { "(Intercept)" : 0.95408999999999999,
      "y" : 0.78297000000000005
    },
  "df.residual" : 3,
  "effects" : { "" : 0.23488999999999999,
      "(Intercept)" : -13.864000000000001,
      "y" : 8.5699000000000005
    },
  "fitted.values" : { "1" : 2.1284999999999998,
      "2" : 2.52,
      "3" : 6.4348999999999998,
      "4" : 7.2179000000000002,
      "5" : 12.699
    },
  "model" : { "x" : [ 1,
          3,
          6,
          9,
          12
        ],
      "y" : [ 1.5,
          2,
          7,
          8,
          15
        ]
    },
  "qr" : { "pivot" : [ 1,
          2
        ],
      "qr" : [ { "(Intercept)" : -2.2361,
            "y" : -14.981999999999999
          },
          { "(Intercept)" : 0.44721,
            "y" : 10.945
          },
          { "(Intercept)" : 0.44721,
            "y" : -0.17422000000000001
          },
          { "(Intercept)" : 0.44721,
            "y" : -0.26557999999999998
          },
          { "(Intercept)" : 0.44721,
            "y" : -0.90512999999999999
          }
        ],
      "qraux" : [ 1.4472,
          1.2826
        ],
      "rank" : 2,
      "tol" : 9.9999999999999995e-08
    },
  "rank" : 2,
  "residuals" : { "1" : -1.1285000000000001,
      "2" : 0.47997000000000001,
      "3" : -0.43489,
      "4" : 1.7821,
      "5" : -0.69865999999999995
    },
  "terms" : [ "~",
      "x",
      "y"
    ],
  "xlevels" : {  }
}

 

Hortonworks DataFlow is an integrated platform that makes data ingestion fast, easy, and secure. Download the white paper now.  Brought to you in partnership with Hortonworks

Topics:

Published at DZone with permission of Gary Sieling, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

The best of DZone straight to your inbox.

SEE AN EXAMPLE
Please provide a valid email address.

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.
Subscribe

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}