stanfordnlp/CoreNLP · error · IllegalArgumentException

Index array length

Error message

Index array length

What it means

Alignment.makeFromIndexArray throws IllegalArgumentException when the length of the index array does not equal hypGraph.size(). Each position i in the array aligns the hypothesis node with index i, so the array must cover every hypothesis node.

Solutions

  1. Recompute the index array against the exact hypGraph instance passed in
  2. Pass the graphs and indexes through the pipeline together so they cannot diverge
  3. Assert indexes.length == hypGraph.size() in caller code before the call

Example fix

// before
int[] indexes = computeIndexes(oldHypGraph);
SemGraph hypGraph = preprocess(oldHypGraph);
Alignment align = Alignment.makeFromIndexArray(txtGraph, hypGraph, indexes, j);
// after
int[] indexes = computeIndexes(hypGraph);
if (indexes.length != hypGraph.size()) { throw new IllegalStateException("stale alignment indexes"); }
Alignment align = Alignment.makeFromIndexArray(txtGraph, hypGraph, indexes, j);
Defensive patterns

Strategy: validation

Validate before calling

if (indexes == null || hypGraph == null || indexes.length != hypGraph.size()) throw new IllegalArgumentException("indexes length must equal hypGraph.size()");

Type guard

boolean indexesMatchGraph(int[] indexes, SemGraph hypGraph) { return indexes != null && hypGraph != null && indexes.length == hypGraph.size(); }

Try / catch

try { Alignment a = Alignment.makeFromIndexArray(txtGraph, hypGraph, indexes, j); } catch (IllegalArgumentException e) { throw new IllegalStateException("Stale alignment indexes: " + e.getMessage(), e); }

Prevention

When it happens

Trigger: Calling Alignment.makeFromIndexArray(txtGraph, hypGraph, indexes, ...) where indexes.length != hypGraph.size(), e.g. after the hypothesis graph was rebuilt or truncated after the array was computed.

Common situations: Graph preprocessed (nodes dropped, collapsed, or re-indexed) after alignment indexes were computed; array built from a different sentence or graph version; off-by-one when filtering empty nodes.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/3a7d260f4c882056. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/semgraph/semgrex/Alignment.java:166

   * {@code SemanticGraph} to the given text (passage) SemanticGraph, using
   * the given array of indexes.  The i'th node of the array should contain the
   * index of the node in the text (passage) SemanticGraph to which the i'th
   * node in the hypothesis SemanticGraph is aligned, or -1 if it is aligned to
   * NO_WORD.
   */
  public static Alignment makeFromIndexArray(SemanticGraph txtGraph,
                                             SemanticGraph hypGraph,
                                             int[] indexes,
                                             double score,
                                             String justification) {
    if (txtGraph == null || txtGraph.isEmpty())
      throw new IllegalArgumentException("Invalid txtGraph " + txtGraph);
    if (hypGraph == null || hypGraph.isEmpty())
      throw new IllegalArgumentException("Invalid hypGraph " + hypGraph);
    if (indexes == null)
      throw new IllegalArgumentException("Null index array");
    if (indexes.length != hypGraph.size())
      throw new IllegalArgumentException("Index array length " + indexes.length +
                                         " does not match hypGraph size " + hypGraph.size());
    Map<IndexedWord, IndexedWord> map =
      Generics.newHashMap();
    for (int i = 0; i < indexes.length; i++) {
      IndexedWord hypNode = hypGraph.getNodeByIndex(i);
      IndexedWord txtNode = IndexedWord.NO_WORD;
      if (indexes[i] >= 0)
        txtNode = txtGraph.getNodeByIndex(indexes[i]);
      map.put(hypNode, txtNode);
    }
    return new Alignment(map, score, justification);
  }

  public static Alignment makeFromIndexArray(SemanticGraph txtGraph,
                                             SemanticGraph hypGraph,
                                             int[] indexes) {
    return makeFromIndexArray(txtGraph, hypGraph, indexes, 0.0, null);
  }

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