Skip to content

Automating Operating Thresholds with WhizzML and the BigML Python Bindings

by on January 26, 2018

This blog post, the fifth of our series of posts about operating thresholdsfocuses on two ways to automate the use of operating thresholds in our predictions (single or batch) and evaluations. The first way involves WhizzML, BigML’s Domain Specific Language for Machine Learning workflow automation. It allows you to execute complex tasks that are computed completely on the server side (with built-in parallelization), where all resources involved are treated as first-class citizens by BigML.

WhizzMLLoop

The second way to automate operating thresholds involves the set of bindings that BigML maintainswhich allow developers to work in their favorite programming language as they interact with the BigML platform. The Python binding is already updated to handle the most recent platform capabilities we’re covering so we’ll use it as an example in this post. However, there are other bindings options such as Java, C# or Node.js.

Operating thresholds can be used with any of your classification models: decision tree models, ensembles, logistic regressions, and deepnets (neural networks). They can improve the quality of your single and batch predictions, and thus, your evaluations.

Let’s see how to automate operating thresholds for a single model by using WhizzML. In our example, we’ll deal with a classifier that has two possible outputs: good or bad. We’re interested in improving the classification of the instances that fall into the good category, so we’ll set this one as the positive class. To ensure that we reduce misclassifications, we’ll consider that our model predicts good only if the probability of this prediction goes over a 60% threshold. To see whether this improves the model’s performance, we can create an evaluation via WhizzML.

;; creates an evaluation setting an operating point 
;; for a single model
(define my-evaluation 
  (create-evaluation {
    "model" my-model
    "dataset" test-dataset
    "operating_point" {
        "kind" "probability"
        "positive_class" "good"
        "threshold" 0.6
    }}))

Remember that almost all BigML resources (except predictions and projects) are asynchronous, so if you want to use the evaluation my-evaluation or its components, like the accuracy, precision, etc., you will need to ensure that the creation process has actually finished. That’s what the next snippet of code does.

;; creates an evaluation with an operating point 
;; for a deepnet and retrieve its precision
(define my-eval-precision 
  (get-in
    (create-and-wait-evaluation {
      "deepnet" my-deepnet
      "dataset" test-dataset
      "operating_point" {
        "kind" "probability"
        "positive_class" "good"
        "threshold" 0.6
      }}) ["result" "model" "precision"]))

If you prefer the BigML Python bindings, the equivalent code is:

from bigml.api import BigML
api = BigML()
args = {
    "operating_point": {
        "kind": "probability", 
        "positive_class": "good",
        "threshold": 0.6
    }
}
my_evaluation = api.create_evaluation(
    "deepnet/59b0f8c7b95b392f12000003",
    "dataset/59b0f8c7b95b392f12000001",
    args)
api.ok(my_evaluation)
precision = my_evaluation["object"]["result"]["model"]["precision"]

For more details about these and other evaluation properties, please check the dedicated API documentation.

Single predictions can also be computed by using this operational threshold. In fact, these evaluations are computed by averaging the matches of single predictions whose outputs are already known. Let’s see how to set a confidence threshold of 0.66 for a prediction made with a logistic regression by using WhizzML.

;; creates a single prediction setting a confidence threshold
(define my-prediction 
  (create-prediction {
    "logisticregression" my-logistic
    "input_data" {"000001" 0.35,"000002" 1.2}
    "operating_point" {
        "kind" "confidence"
        "positive_class" "good"
        "threshold" 0.66
    }}))

These plus other prediction properties are also explained in the API documentation. Using the BigML Python bindings, the equivalent code would be as follows:

from bigml.api import BigML
api = BigML()
args = {
    "operating_point": {
        "kind": "confidence", 
        "positive_class": "good",
        "threshold": 0.66 
    }
}
input_data = {"000001": 0.35,"000002": 1.2}
logistic_id = "logisticregression/59b0f8c7b95b392f12000000"
my_prediction = api.create_prediction(logistic_id, input_data, args)

As we mentioned above, you can also use operating thresholds for your batch predictions. Below you can see how to create a batch prediction in WhizzML by using an ensemble of ten models, where we specify that at least six models should return the positive class in their predictions.

;; creates a batch prediction setting
;; a threshold based on the number of votes
(define my-batchprediction
  (create-batchprediction {
    "ensemble" my_ensemble
    "dataset" my_dataset
    "operating_point" {
        "kind" "votes"
        "positive_class" "good"
        "threshold" 6
    }}))

With the BigML Python bindings, you should write this code as:

from bigml.api import BigML
api = BigML()
args = {
    "operating_point": {
        "kind": "votes", 
        "positive_class": "good",
        "threshold": 6
    }
}
ensemble = "ensemble/59b0f8c7b95b392f12000001"
dataset = "dataset/59b0f8c7b95b392f12000003"
my_batch_prediction = api.create_batch_prediction(ensemble, dataset, args)

Easy, right? If it’s your first time using our Domain Specific Language for Machine Learning we recommend that you check this series of blog posts to get familiarized with WhizzML.

Want to know more about operating thresholds?

If you have any questions or you’d like to learn more about how operating thresholds work, please visit the dedicated release page. It includes a series of six blog posts about operating thresholds, the BigML Dashboard and API documentation, the webinar slideshow as well as the full webinar recording.

2 Comments
  1. That kind of thkinnig shows you’re on top of your game

Trackbacks & Pingbacks

  1. Introduction to Operating Thresholds | The Official Blog of BigML.com

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s

%d bloggers like this: