title: LightGBMError: b'Check failed: config->bagging_freq > 0 && config->bagging_fraction < 1.0f && config->bagging_fraction > 0.0f
body: <p>Working with lightGBM on Python and as it doesn't have enough documentation, I am unable to tackle this issue since a while. Please help me out with these few questions if anyone with lgb experience available here. </p>
  
  <ol>
  <li>lgb.cv doesn't work when having a continuous target variable. Why?</li>
  <li>When having objective "regression" can I have boosting_type as "rf" (random Forest)? This <a href="https://github.com/Microsoft/LightGBM/issues/1246" rel="nofollow noreferrer">issue</a> opened here on the library kinda confirms that I can. Thoughts?</li>
  <li><p>Below is the piece of code that works completely fine if I replace the "rf" parameter with "gbdt"</p>
  
  <pre><code>params = {
          "objective" : "regression", "metric" : "rmse",
          "num_leaves" : 150, "learning_rate" : 0.05,
          "bagging_fraction" : 0.6, "feature_fraction" : 0.7,
          "bagging_frequency" : 1, "bagging_seed" : 2018,
          "verbosity" : -1, 'max_depth':-1,
          "min_child_samples":20, "boosting":"rf"}
  
  model = lgb.train(params, lgtrain, 1000, valid_sets=[lgval],
          early_stopping_rounds=20, verbose_eval=20, evals_result=evals_result)
  </code></pre></li>
  </ol>
  
  <p><strong>On having random forest boosting method, I get the following error -</strong></p>
  
  <pre><code>LightGBMError: b'Check failed: config-&gt;bagging_freq &gt; 0 &amp;&amp; config-&gt;bagging_fraction &lt; 1.0f &amp;&amp; config-&gt;bagging_fraction &gt; 0.0f at /home/travis/build/Microsoft/LightGBM/python-package/compile/src/boosting/rf.hpp, line 29 .\n'
  </code></pre>