Regressor Model — `mlRegressorModel`

Compare regression algorithms and their error on held-out folds before fitting a final model.

What it does

Reads the incoming column schema and emits an unfitted model definition on its model output. It carries the algorithm, target, feature names, hyperparameters and preprocessing. The definition does not fit the data, create an MLflow run or save a trained artifact; model_uri and mlflow_run_id are null.

Connect the same dataset to this node's in input and to Cross-Validate's in input. Connect this node's purple model output to Cross-Validate's model input. Cross-Validate builds and fits a fresh pipeline within each fold. Definition nodes do not have a data output.

This node accepts regression models only. It has no training-row minimum, because it does not train; Cross-Validate requires at least ten incoming rows. The target and selected features must exist, the target cannot also be a feature, and the configured feature-count limit applies.

Configuration

Config key	Type	Required	Description
`model_type`	string	Yes	An algorithm for this node's task; editor default: `ridge`
`target_column`	string	Yes	Existing target column; the editor starts blank
`feature_columns`	string[]	No	Existing predictors; omitted or `[]` selects all columns except the target
`hyperparameters`	object	No	Algorithm-specific settings; defaults to `{}` and then the estimator defaults
`preprocessing`	object	No	Numeric/categorical column lists, imputation and scaling; see below
`seed`	integer	Yes	Reproducibility seed; editor default `42`

With empty or omitted preprocessing, numeric and categorical columns are inferred from the chosen features. Numeric columns use median imputation and standard scaling; categorical columns use most-frequent imputation and one-hot encoding. For an explicit nonempty preprocessing object, supply numeric_columns and/or categorical_columns: missing lists are empty. If both lists are empty, the estimator receives the raw features without preprocessing.

Numeric options are numeric_strategy (standard_scaler, minmax_scaler, robust_scaler, or another value to omit scaling) and impute_numeric (default median). Categorical imputation uses impute_categorical (default most_frequent). These steps are fitted inside each Cross-Validate fold.

Generated Python code

Download the customer sample CSV and save it as customers.csv in the directory where you run the script. These complete exports define a ridge model and send it to three-fold K-Fold Cross-Validate, then write regressor-model-scores.csv.

The target is monthly_charges and the features are tenure, support_calls; the customer ID is excluded. The output has three rows containing the fold number, R², root mean squared error and actual fit time. The sample is a small demonstration, so its scores are not evidence of model quality on a real customer population. Fit times vary between executions.

The definition-node configuration is:

json

{
  "model_type": "ridge",
  "target_column": "monthly_charges",
  "feature_columns": [
    "tenure",
    "support_calls"
  ],
  "seed": 42
}

The Cross-Validate configuration is cv_strategy="kfold", n_splits=3 and seed=42. Both flow engines use pandas/scikit-learn at the ML boundary. Run the export in an environment with Ciaren installed: Cross-Validate imports Ciaren's registered model builder (app.ml.models). It does not create a final model artifact or contact an MLflow tracking service.

pandas

python

import pandas as pd
import json
from app.ml.models import build_estimator
from sklearn.compose import ColumnTransformer
from sklearn.impute import SimpleImputer
from sklearn.model_selection import cross_validate, KFold
from sklearn.pipeline import Pipeline
from sklearn.preprocessing import MinMaxScaler, OneHotEncoder, RobustScaler, StandardScaler

df_customers = pd.read_csv('customers.csv')
_model_config = {'model_type': 'ridge', 'target_column': 'monthly_charges', 'feature_columns': ['tenure', 'support_calls'], 'hyperparameters': None, 'preprocessing': None, 'seed': 42}
_model_config['feature_columns'] = _model_config['feature_columns'] or [c for c in df_customers.columns if c != _model_config['target_column']]
_model_config['hyperparameters'] = _model_config['hyperparameters'] or {}
_model_config['preprocessing'] = _model_config['preprocessing'] or {}
df_1 = pd.DataFrame([{'mlflow_run_id': None, 'model_uri': None, 'task_type': 'regression', 'model_type': 'ridge', 'target_column': _model_config['target_column'], 'feature_columns_json': json.dumps(_model_config['feature_columns']), 'model_config_json': json.dumps(_model_config)}])
_model_ref = df_1.iloc[0]
_model_config = json.loads(_model_ref['model_config_json'])
_task = _model_ref.get('task_type')
_target = _model_config['target_column']
_features = _model_config.get('feature_columns') or [c for c in df_customers.columns if c != _target]
_X = df_customers[_features]
_y = df_customers[_target]
_pre = _model_config.get('preprocessing') or {}
if _pre:
    _numeric = _pre.get('numeric_columns', [])
    _categorical = _pre.get('categorical_columns', [])
else:
    _numeric = [c for c in _features if pd.api.types.is_numeric_dtype(_X[c])]
    _categorical = [c for c in _features if c not in _numeric]
_num_strategy = _pre.get('numeric_strategy', 'standard_scaler')
_scalers = {
    'standard_scaler': StandardScaler,
    'minmax_scaler': MinMaxScaler,
    'robust_scaler': RobustScaler,
}
_transformers = []
if _numeric:
    _num_steps = [('impute', SimpleImputer(strategy=_pre.get('impute_numeric', 'median')))]
    if _num_strategy in _scalers:
        _num_steps.append(('scale', _scalers[_num_strategy]()))
    _transformers.append(('num', Pipeline(_num_steps), _numeric))
if _categorical:
    _cat_steps = [
        ('impute', SimpleImputer(strategy=_pre.get('impute_categorical', 'most_frequent'))),
        ('encode', OneHotEncoder(handle_unknown='ignore')),
    ]
    _transformers.append(('cat', Pipeline(_cat_steps), _categorical))
_steps = []
if _transformers:
    _steps.append(('preprocessor', ColumnTransformer(_transformers, remainder='drop')))
_estimator = build_estimator(
    _model_config['model_type'],
    _model_config.get('hyperparameters'),
    _model_config.get('seed'),
)
_steps.append(('model', _estimator))
_pipeline = Pipeline(_steps)
_cv = KFold(n_splits=3, shuffle=True, random_state=42)
_scoring = []
if not _scoring:
    if _task == 'classification':
        _scoring = ['accuracy', 'f1_weighted']
    else:
        _scoring = ['r2', 'neg_root_mean_squared_error']
_scores = cross_validate(_pipeline, _X, _y, cv=_cv, scoring=_scoring, return_train_score=False)
_rows = []
_n_folds = len(_scores['fit_time'])
for _i in range(_n_folds):
    _row = {'fold': _i + 1}
    for _m in _scoring:
        _v = _scores['test_' + _m][_i]
        _row[_m[4:] if _m.startswith('neg_') else _m] = -_v if _m.startswith('neg_') else _v
    _row['fit_time_s'] = _scores['fit_time'][_i]
    _rows.append(_row)
df_2 = pd.DataFrame(_rows)
df_2.to_csv('regressor-model-scores.csv', index=False)

Polars

python

import polars as pl
import json
import pandas as pd
from app.ml.models import build_estimator
from sklearn.compose import ColumnTransformer
from sklearn.impute import SimpleImputer
from sklearn.model_selection import cross_validate, KFold
from sklearn.pipeline import Pipeline
from sklearn.preprocessing import MinMaxScaler, OneHotEncoder, RobustScaler, StandardScaler

df_customers = pl.read_csv('customers.csv')
_eager_1 = df_customers.to_pandas()
_model_config = {'model_type': 'ridge', 'target_column': 'monthly_charges', 'feature_columns': ['tenure', 'support_calls'], 'hyperparameters': None, 'preprocessing': None, 'seed': 42}
_model_config['feature_columns'] = _model_config['feature_columns'] or [c for c in _eager_1.columns if c != _model_config['target_column']]
_model_config['hyperparameters'] = _model_config['hyperparameters'] or {}
_model_config['preprocessing'] = _model_config['preprocessing'] or {}
_eager_2 = pd.DataFrame([{'mlflow_run_id': None, 'model_uri': None, 'task_type': 'regression', 'model_type': 'ridge', 'target_column': _model_config['target_column'], 'feature_columns_json': json.dumps(_model_config['feature_columns']), 'model_config_json': json.dumps(_model_config)}])
_eager_3 = df_customers.to_pandas()
_model_ref = _eager_2.iloc[0]
_model_config = json.loads(_model_ref['model_config_json'])
_task = _model_ref.get('task_type')
_target = _model_config['target_column']
_features = _model_config.get('feature_columns') or [c for c in _eager_3.columns if c != _target]
_X = _eager_3[_features]
_y = _eager_3[_target]
_pre = _model_config.get('preprocessing') or {}
if _pre:
    _numeric = _pre.get('numeric_columns', [])
    _categorical = _pre.get('categorical_columns', [])
else:
    _numeric = [c for c in _features if pd.api.types.is_numeric_dtype(_X[c])]
    _categorical = [c for c in _features if c not in _numeric]
_num_strategy = _pre.get('numeric_strategy', 'standard_scaler')
_scalers = {
    'standard_scaler': StandardScaler,
    'minmax_scaler': MinMaxScaler,
    'robust_scaler': RobustScaler,
}
_transformers = []
if _numeric:
    _num_steps = [('impute', SimpleImputer(strategy=_pre.get('impute_numeric', 'median')))]
    if _num_strategy in _scalers:
        _num_steps.append(('scale', _scalers[_num_strategy]()))
    _transformers.append(('num', Pipeline(_num_steps), _numeric))
if _categorical:
    _cat_steps = [
        ('impute', SimpleImputer(strategy=_pre.get('impute_categorical', 'most_frequent'))),
        ('encode', OneHotEncoder(handle_unknown='ignore')),
    ]
    _transformers.append(('cat', Pipeline(_cat_steps), _categorical))
_steps = []
if _transformers:
    _steps.append(('preprocessor', ColumnTransformer(_transformers, remainder='drop')))
_estimator = build_estimator(
    _model_config['model_type'],
    _model_config.get('hyperparameters'),
    _model_config.get('seed'),
)
_steps.append(('model', _estimator))
_pipeline = Pipeline(_steps)
_cv = KFold(n_splits=3, shuffle=True, random_state=42)
_scoring = []
if not _scoring:
    if _task == 'classification':
        _scoring = ['accuracy', 'f1_weighted']
    else:
        _scoring = ['r2', 'neg_root_mean_squared_error']
_scores = cross_validate(_pipeline, _X, _y, cv=_cv, scoring=_scoring, return_train_score=False)
_rows = []
_n_folds = len(_scores['fit_time'])
for _i in range(_n_folds):
    _row = {'fold': _i + 1}
    for _m in _scoring:
        _v = _scores['test_' + _m][_i]
        _row[_m[4:] if _m.startswith('neg_') else _m] = -_v if _m.startswith('neg_') else _v
    _row['fit_time_s'] = _scores['fit_time'][_i]
    _rows.append(_row)
_eager_4 = pd.DataFrame(_rows)
df_1 = pl.from_pandas(_eager_4)
df_1.write_csv('regressor-model-scores.csv')

Tips and common mistakes

Use a definition for evaluation; use a Train node when you need a saved model for Predict or Feature Importance. A definition cannot supply fitted predictions.
List predictors explicitly when the input includes IDs or columns that would leak the answer. Empty feature_columns includes every non-target column, including IDs.
When configuring preprocessing explicitly, include the column lists. Setting only a scaling strategy leaves no selected preprocessing columns.
Keep standalone feature engineering out of the evaluation's full-data branch when it learns from the data. Put imputation, scaling and encoding in the model definition so they are fitted within each fold.