#
Adding a Custom Task

Lighteval provides a flexible framework for creating custom evaluation tasks. This guide explains how to create and integrate new tasks into the evaluation system.

##
Step-by-Step Creation of a Task

> To contribute your task to the Lighteval repository, you would first need to install the required dev dependencies by running `pip install -e .[dev]` and then run `pre-commit install` to install the pre-commit hooks.

###
Step 1: Create the Task File

First, create a Python file or directory under the `src/lighteval/tasks/tasks` directory. A directory is helpfull if you need to split your file into multiple ones, just make sure to have one of the file named `main.py`.

###
Step 2: Define the Prompt Function

You need to define a prompt function that will convert a line from your dataset to a document to be used for evaluation.

    from lighteval.tasks.requests import Doc

    # Define as many as you need for your different tasks
    def prompt_fn(line: dict, task_name: str):
        """Defines how to go from a dataset line to a doc object.
        Follow examples in src/lighteval/tasks/default_prompts.py, or get more info
        about what this function should do in the README.
        """
        return Doc(
            task_name=task_name,
            query=line["question"],
            choices=[f" {c}" for c in line["choices"]],
            gold_index=line["gold"],
        )

###
Step 3: Choose or Create Metrics

You can either use an existing metric (defined in `lighteval.metrics.metrics.Metrics`) or create a custom one.

####
Using Existing Metrics

    from lighteval.metrics import Metrics

    # Use an existing metric
    metric = Metrics.ACCURACY

####
Creating Custom Metrics

    from lighteval.metrics.utils.metric_utils import SampleLevelMetric
    import numpy as np

    custom_metric = SampleLevelMetric(
        metric_name="my_custom_metric_name",
        higher_is_better=True,
        category="accuracy",
        sample_level_fn=lambda x: x,  # How to compute score for one sample
        corpus_level_fn=np.mean,  # How to aggregate the sample metrics
    )

###
Step 4: Define Your Task

You can define a task with or without subsets using LightevalTaskConfig.

####
Simple Task (No Subsets)

    from lighteval.tasks.lighteval_task import LightevalTaskConfig

    # This is how you create a simple task (like HellaSwag) which has one single subset
    # attached to it, and one evaluation possible.
    task = LightevalTaskConfig(
        name="myothertask",
        prompt_function=prompt_fn,  # Must be defined in the file or imported
        hf_repo="your_dataset_repo_on_hf",
        hf_subset="default",
        hf_avail_splits=["train", "test"],
        evaluation_splits=["test"],
        few_shots_split="train",
        few_shots_select="random_sampling_from_train",
        metrics=[metric],  # Select your metric in Metrics
        generation_size=256,
        stop_sequence=["\n", "Question:"],
    )

####
Task with Multiple Subsets

If you want to create a task with multiple subsets, add them to the `SAMPLE_SUBSETS` list and create a task for each subset.

    SAMPLE_SUBSETS = ["subset1", "subset2", "subset3"]  # List of all the subsets to use for this eval

    class CustomSubsetTask(LightevalTaskConfig):
        def __init__(
            self,
            name,
            hf_subset,
        ):
            super().__init__(
                name=name,
                hf_subset=hf_subset,
                prompt_function=prompt_fn,  # Must be defined in the file or imported
                hf_repo="your_dataset_name",
                metrics=[custom_metric],  # Select your metric in Metrics or use your custom_metric
                hf_avail_splits=["train", "test"],
                evaluation_splits=["test"],
                few_shots_split="train",
                few_shots_select="random_sampling_from_train",
                generation_size=256,
                stop_sequence=["\n", "Question:"],
            )

    SUBSET_TASKS = [CustomSubsetTask(name=f"task:{subset}", hf_subset=subset) for subset in SAMPLE_SUBSETS]

###
Step 5: Add Tasks to the Table

Then you need to add your task to the `TASKS_TABLE` list.

    # STORE YOUR EVALS

    # Tasks with subsets:
    TASKS_TABLE = SUBSET_TASKS

    # Tasks without subsets:
    # TASKS_TABLE = [task]

###
Step 6: Creating a requirement file

If your task has requirements, you need to create a `requirement.txt` file with only the required dependencies so that anyone can run your task.

##
Running Your Custom Task

Once your file is created, you can run the evaluation with the following command:

    lighteval accelerate \
        "model_name=HuggingFaceH4/zephyr-7b-beta" \
        {task} \
        --custom-tasks {path_to_your_custom_task_file}

###
Example Usage

    # Run a custom task with 3 shot evaluation
    lighteval accelerate \
        "model_name=openai-community/gpt2" \
        "myothertask|3" \
        --custom-tasks community_tasks/my_custom_task.py

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