From 6618b269933a363af1b73714df8a07832cdcc2ec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rn=20Kottmann?= <joern@apache.org>
Date: Sun, 29 Jan 2017 11:44:48 +0100
Subject: [PATCH] OPENNLP-371: Throw an exception if training data only has one
 outcome

---
 .../main/java/opennlp/tools/ml/AbstractEventTrainer.java    | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/opennlp-tools/src/main/java/opennlp/tools/ml/AbstractEventTrainer.java b/opennlp-tools/src/main/java/opennlp/tools/ml/AbstractEventTrainer.java
index b73df3717..c465f889c 100644
--- a/opennlp-tools/src/main/java/opennlp/tools/ml/AbstractEventTrainer.java
+++ b/opennlp-tools/src/main/java/opennlp/tools/ml/AbstractEventTrainer.java
@@ -25,6 +25,7 @@
 import opennlp.tools.ml.model.Event;
 import opennlp.tools.ml.model.HashSumEventStream;
 import opennlp.tools.ml.model.MaxentModel;
+import opennlp.tools.util.InsufficientTrainingDataException;
 import opennlp.tools.util.ObjectStream;
 import opennlp.tools.util.TrainingParameters;
 
@@ -68,6 +69,11 @@ public final MaxentModel train(DataIndexer indexer) throws IOException {
     if (!isValid()) {
       throw new IllegalArgumentException("trainParams are not valid!");
     }
+
+    if (indexer.getOutcomeLabels().length <= 1) {
+      throw new InsufficientTrainingDataException("Training data must contain more than one outcome");
+    }
+
     MaxentModel model = doTrain(indexer);
     addToReport(AbstractTrainer.TRAINER_TYPE_PARAM, EventTrainer.EVENT_VALUE);
     return model;