Rclipper is a package for building serveable Clipper models from R functions. Given an API-compatible R function, Rclipper’s build_model function builds a Docker image for a Clipper model. This model can then be deployed to Clipper via the Python clipper_admin package.


Rclipper depends on the Python clipper_admin package for building and deploying models. In order to use this admin package, Docker for Python must also be installed.

Importing Rclipper

It is very important that Rclipper be imported before a prediction function or its dependencies are defined. Rclipper makes use of the histry package to statically analyze dependency definitions. In order to locate these definition expressions during function serialization, histry must be imported before the expressions are executed.

Writing an API-compatible R prediction function

An API-compatible prediction function must accept a type-homogeneous list of inputs of one of the following types:

  • Raw Vector
  • Integer Vector
  • Numeric Vector
  • String (length-1 character vector)
  • Data Frame
  • Matrix
  • Array
  • List

Additionally, given a list of inputs of length N, a prediction function must return a list of outputs of length N. All elements of the output list must be of the same type.

Note: If a prediction function returns a list of string (length-1 character vector) objects, each output will be returned as-is, without any additional serialization. Otherwise, all non-string outputs will be string-serialized via the jsonlite package, and their serialized representations will be returned.

Building a model

Once you’ve written an API-compatible prediction function, you can build a Clipper model with it via the build_model function:

#' @param model_name character vector of length 1. The name to assign to the model image.
#' @param model_version character vector of length 1. The version tag to assign to the model image.
#' @param prediction_function function. This should accept a type-homogeneous list of
#' inputs and return a list of outputs of the same length. If the elements of the output list
#' are not character vectors of length 1, they will be converted to a serialized
#' string representation via 'jsonlite'.
#' @param sample_input For a prediction function that accepts a list of inputs of type X,
#' this should be a single input of type X. This is used to validate the compatability
#' of the function with Clipper and to determine the Clipper data type (bytes, ints, strings, etc)
#' to associate with the model.
#' @param model_registry character vector of length 1. The name of the image registry
#' to which to upload the model image. If NULL, the image will not be uploaded to a registry.

Rclipper::build_model(model_name, model_version, prediction_function, sample_input, model_registry = NULL)

This will build a Docker image with the tag: model_registry/model_name:model_version. If no registry was specified, the image will have the tag: model_name:model_version. Additonally, this function will output a command that you can execute within an interactive Python environment to deploy the model with the clipper_admin package.

Deploying a model

Once you’ve built a model, use the provided command to deploy it with the clipper_admin package. For information about how to register the model with an application so that it can be queried, please consult the clipper_admin API documentation.

Querying a model

After you’ve built a model, deployed the model, and registered the model with an application, you can query it with input data of the correct type. The following table maps the input type of your model’s prediction function to the Clipper input type associated with your deployed model:

R input type

Clipper Input Type

JSON Format


Raw Vector


Base64-encoded string


Integer Vector


Integer array


Numeric Vector


Floating point array


Character Vector



“input text”

Data Frame

















Import Rclipper


## Loading required package: CodeDepends

## Loading required package: histry

Define an API-compatible prediction function

#' Given a list of vector inputs,
#' outputs a list containing the
#' length of each input vector as a string
pred_fn = function(inputs) {
return(lapply(inputs, function(input) {

print(pred_fn(list(c(1,2), c(3))))

## [[1]]
## [1] "2"
## [[2]]
## [1] "1"

Build a model

# Specify that the prediction function expects integer vectors
# by supplying an integer vector as the sample input
Rclipper::build_model("test-model", "1", pred_fn, sample_input = as.integer(c(1,2,3)))

## [1] "Serialized list of dependent libraries: Rclipper: knitr: histry: CodeDepends: stats: graphics: grDevices: utils: datasets: methods: base"
## [1] "Serialized model function!"
## [1] "Done!"
## To deploy this model, execute the following command from a connected ClipperConnection object `conn`:
## conn.deploy_model("test-model", "1", "ints", "test-model:1", num_replicas=<num_container_replicas>)

Query the model

You can now query the model from any HTTP client. For example, directly from the command line with cURL:

$ curl -X POST --header "Content-Type:application/json" -d '{"input": [1,2,3,4]}'

$ {"query_id":2,"output":4,"default":false}