User attributes

Annotate a study or an individual trial with your own metadata — a dataset name, the git commit, a secondary metric you want to keep alongside the objective. Attributes are key/value pairs; the key is a string and the value should be JSON-serializable so it survives a round-trip through persistent storage.

Adding attributes to a study

Study.SetUserAttr registers one attribute; Study.UserAttrs reads them back.

using OptunaSharp;
using OptunaSharp.Storages;

using var storage = new RDBStorage("sqlite:///example.db");
var study = Optuna.CreateStudy(storage: storage);

study.SetUserAttr("contributors", new[] { "Akiba", "Sano" });
study.SetUserAttr("dataset", "MNIST");

foreach (var (key, value) in study.UserAttrs)
    Console.WriteLine($"{key} = {value}");
// contributors = [Akiba, Sano]
// dataset = MNIST

A StudySummary, which you get from Optuna.GetAllStudySummaries, also carries the study's attributes — handy for listing studies without loading each one:

foreach (StudySummary summary in Optuna.GetAllStudySummaries(storage))
    Console.WriteLine(summary.UserAttrs["dataset"]);

The optunasharp study set-user-attr command sets a study attribute from the shell.

Adding attributes to a trial

A trial has the same method. Set attributes from inside the objective to record per-trial context — here, a secondary metric computed alongside the objective:

double Objective(Trial trial)
{
    double svcC = trial.SuggestFloat("svc_c", 1e-10, 1e10, log: true);
    double accuracy = TrainAndScore(svcC);        // your model here

    trial.SetUserAttr("accuracy", accuracy);       // keep the raw accuracy…
    return 1.0 - accuracy;                          // …while minimizing error
}

study.Optimize(Objective, nTrials: 1);

// Read it back from the stored trial:
Console.WriteLine(study.Trials[0].UserAttrs["accuracy"]);

The attribute is attached to that single FrozenTrial, not to the study.

Relationship to Optuna

Optuna (Python)	OptunaSharp
study.set_user_attr("dataset", "MNIST")	study.SetUserAttr("dataset", "MNIST")
study.user_attrs	study.UserAttrs
optuna.get_all_study_summaries("sqlite:///example.db")	Optuna.GetAllStudySummaries(storage)
trial.set_user_attr("accuracy", acc)	trial.SetUserAttr("accuracy", acc)
study.trials[0].user_attrs	study.Trials[0].UserAttrs

Note the one API-shape difference: GetAllStudySummaries takes a storage instance, not a URL string. Construct the RDBStorage and pass it.

See also

Study and Trials · Storage · Command-line interface · the API reference.