Improving the multiple response documentation in CSVLoader

Core/src/test/java/org/tribuo/test/MockMultiOutput.java

@@ -231,11 +231,13 @@ public String toString() {
         StringBuilder builder = new StringBuilder();
 
         builder.append("(LabelSet={");
-        for (MockOutput l : labels) {
-            builder.append(l.toString());
-            builder.append(',');
+        if (labels.size() > 0) {
+            for (MockOutput l : labels) {
+                builder.append(l.toString());
+                builder.append(',');
+            }
+            builder.deleteCharAt(builder.length() - 1);
         }
-        builder.deleteCharAt(builder.length()-1);
         builder.append('}');
         if (!Double.isNaN(score)) {
             builder.append(",OverallScore=");

Data/src/main/java/org/tribuo/data/csv/CSVLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2022, Oracle and/or its affiliates. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -68,6 +68,12 @@
  * {@link org.tribuo.data.columnar.RowProcessor} to cope with your specific input format.
  * <p>
  * CSVLoader is thread safe and immutable.
+ * <p>
+ * Multi-output responses such as {@code MultiLabel} or {@code Regressor} can be processed in
+ * two different ways either as a single column of separated values, or multiple columns. If
+ * there is a single column the value is passed directly to the {@link OutputFactory}. If
+ * there are multiple response columns then the name of the column is concatenated with the
+ * value, then a list of the concatenated values is passed to the {@link OutputFactory}.
  * @param <T> The type of the output generated.
  */
 public class CSVLoader<T extends Output<T>> {
@@ -139,6 +145,10 @@ public MutableDataset<T> load(Path csvPath, String responseName, String[] header
      * <p>
      * The {@code responseNames} set is traversed in iteration order to emit outputs,
      * and should be an ordered set to ensure reproducibility.
+     * <p>
+     * If there are multiple elements in {@code responseNames} then the responses are
+     * processed into the form 'column-name=column-value' before being passed to the
+     * {@link OutputFactory} for conversion into an {@link Output}.
      *
      * @param csvPath       The path to load.
      * @param responseNames The names of the response variables.
@@ -154,6 +164,10 @@ public MutableDataset<T> load(Path csvPath, Set<String> responseNames) throws IO
      * <p>
      * The {@code responseNames} set is traversed in iteration order to emit outputs,
      * and should be an ordered set to ensure reproducibility.
+     * <p>
+     * If there are multiple elements in {@code responseNames} then the responses are
+     * processed into the form 'column-name=column-value' before being passed to the
+     * {@link OutputFactory} for conversion into an {@link Output}.
      *
      * @param csvPath       The path to load.
      * @param responseNames The names of the response variables.
@@ -220,6 +234,10 @@ public DataSource<T> loadDataSource(URL csvPath, String responseName, String[] h
      * <p>
      * The {@code responseNames} set is traversed in iteration order to emit outputs,
      * and should be an ordered set to ensure reproducibility.
+     * <p>
+     * If there are multiple elements in {@code responseNames} then the responses are
+     * processed into the form 'column-name=column-value' before being passed to the
+     * {@link OutputFactory} for conversion into an {@link Output}.
      *
      * @param csvPath       The csv to load from.
      * @param responseNames The names of the response variables.
@@ -235,6 +253,10 @@ public DataSource<T> loadDataSource(Path csvPath, Set<String> responseNames) thr
      * <p>
      * The {@code responseNames} set is traversed in iteration order to emit outputs,
      * and should be an ordered set to ensure reproducibility.
+     * <p>
+     * If there are multiple elements in {@code responseNames} then the responses are
+     * processed into the form 'column-name=column-value' before being passed to the
+     * {@link OutputFactory} for conversion into an {@link Output}.
      *
      * @param csvPath       The csv to load from.
      * @param responseNames The names of the response variables.
@@ -250,6 +272,10 @@ public DataSource<T> loadDataSource(URL csvPath, Set<String> responseNames) thro
      * <p>
      * The {@code responseNames} set is traversed in iteration order to emit outputs,
      * and should be an ordered set to ensure reproducibility.
+     * <p>
+     * If there are multiple elements in {@code responseNames} then the responses are
+     * processed into the form 'column-name=column-value' before being passed to the
+     * {@link OutputFactory} for conversion into an {@link Output}.
      *
      * @param csvPath       The csv to load from.
      * @param responseNames The names of the response variables.
@@ -266,6 +292,10 @@ public DataSource<T> loadDataSource(Path csvPath, Set<String> responseNames, Str
      * <p>
      * The {@code responseNames} set is traversed in iteration order to emit outputs,
      * and should be an ordered set to ensure reproducibility.
+     * <p>
+     * If there are multiple elements in {@code responseNames} then the responses are
+     * processed into the form 'column-name=column-value' before being passed to the
+     * {@link OutputFactory} for conversion into an {@link Output}.
      *
      * @param csvPath       The csv to load from.
      * @param responseNames The names of the response variables.

Data/src/test/java/org/tribuo/data/csv/CSVLoaderTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2022, Oracle and/or its affiliates. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -82,13 +82,21 @@ public void testLoadMultiOutput() throws IOException {
         assertTrue(data.getExample(1).getOutput().contains("R1"));
         assertTrue(data.getExample(1).getOutput().contains("R2"));
 
-
         //
         // Row #2: R1=False and R2=False.
         // In this case, the labelSet is empty and the labelString is the empty string.
         assertEquals(0, data.getExample(2).getOutput().getLabelSet().size());
         assertEquals("", data.getExample(2).getOutput().getLabelString());
         assertTrue(data.getExample(2).validateExample());
+
+        URL singlePath = CSVLoaderTest.class.getResource("/org/tribuo/data/csv/test-multioutput-singlecolumn.csv");
+        DataSource<MockMultiOutput> singleSource = loader.loadDataSource(singlePath, "Label");
+        MutableDataset<MockMultiOutput> singleData = new MutableDataset<>(singleSource);
+        assertEquals(6, singleData.size());
+
+        for (int i = 0; i < 6; i++) {
+            assertEquals(data.getExample(i).getOutput().getLabelString(), singleData.getExample(i).getOutput().getLabelString());
+        }
     }
 
     @Test

Data/src/test/resources/org/tribuo/data/csv/test-multioutput-singlecolumn.csv

@@ -0,0 +1,7 @@
+A,B,C,D,Label
+1,2,3,4,"R1"
+6,7,8,9,"R1,R2"
+6,7,8,9,
+2,5,3,4,"R1"
+1,2,5,9,"R2"
+0,2,5,9,"R2"

MultiLabel/Core/src/main/java/org/tribuo/multilabel/MultiLabel.java

@@ -314,11 +314,13 @@ public String toString() {
         StringBuilder builder = new StringBuilder();
 
         builder.append("(LabelSet={");
-        for (Label l : labels) {
-            builder.append(l.toString());
-            builder.append(',');
+        if (labels.size() > 0) {
+            for (Label l : labels) {
+                builder.append(l.toString());
+                builder.append(',');
+            }
+            builder.deleteCharAt(builder.length() - 1);
         }
-        builder.deleteCharAt(builder.length()-1);
         builder.append('}');
         if (!Double.isNaN(score)) {
             builder.append(",OverallScore=");