apache/druid · error · RE

Failed to parse array element

Error message

Failed to parse array element %s as a double

What it means

Thrown while parsing a typed double array literal when an element token is neither a LONG nor a DOUBLE literal (and not NULL), so it cannot be converted to a double. Indicates malformed array-literal syntax that the grammar accepted structurally but cannot coerce.

Solutions

1. Remove or fix the offending element reported in the message so it is a plain numeric literal or NULL
2. Use an untyped ARRAY literal or a string array if the data is not numeric
3. Convert string values with a cast, e.g. ARRAY<DOUBLE>[CAST('1.5' AS DOUBLE)] via appropriate expression forms

Example fix

// before
ARRAY<DOUBLE>['1.5', 2]
// after
ARRAY<DOUBLE>[1.5, 2.0]

// Java: validate double-array literal elements before emitting the expression
static boolean isValidDoubleArrayLiteral(java.util.List<String> elems) {
  return elems.stream().allMatch(e -> {
    try { com.google.common.primitives.Doubles.tryParse(e.replace("NULL","").trim()); return true; }
    catch (Exception ex) { return false; }
  });
}

When it happens

Trigger: Parsing an expression like ARRAY<DOUBLE>[abc] or a double array containing string/boolean elements; numeric elements that fail Numbers.parseDoubleObject (e.g. out-of-range or malformed).

Common situations: Hand-written expression filters/aggregations with quoted or non-numeric elements in typed double arrays; generated expressions from upstream tools emitting strings into numeric arrays.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Failed to convert array type
• Failed to parse array element
• Failed to parse array element
• Failed to parse array element
• Failed to parse array: element

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/bf3ad74d5d158ae9. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/math/expr/ExprListenerImpl.java:403

  @Override
  public void exitNull(ExprParser.NullContext ctx)
  {
    nodes.put(ctx, new NullLongExpr());
  }

  @Override
  public void exitDoubleArray(ExprParser.DoubleArrayContext ctx)
  {
    Object[] values = new Object[ctx.numericElement().size()];
    for (int i = 0; i < values.length; i++) {
      if (ctx.numericElement(i).NULL() != null) {
        values[i] = null;
      } else if (ctx.numericElement(i).LONG() != null) {
        values[i] = Numbers.parseDoubleObject(ctx.numericElement(i).LONG().getText());
      } else if (ctx.numericElement(i).DOUBLE() != null) {
        values[i] = Numbers.parseDoubleObject(ctx.numericElement(i).DOUBLE().getText());
      } else {
        throw new RE("Failed to parse array element %s as a double", ctx.numericElement(i).getText());
      }
    }
    nodes.put(ctx, new ArrayExpr(ExpressionType.DOUBLE_ARRAY, values));
  }

  @Override
  public void exitExplicitArray(ExprParser.ExplicitArrayContext ctx)
  {
    ExpressionType type = ExpressionType.fromString(ctx.ARRAY_TYPE().getText());
    if (type == null) {
      throw new RE("Failed to convert array type %s to expression type", ctx.ARRAY_TYPE().getText());
    }
    Object[] values = new Object[ctx.literalElement().size()];
    for (int i = 0; i < values.length; i++) {
      if (ctx.literalElement(i).NULL() != null) {
        values[i] = null;
      } else {
        final ExprParser.LiteralElementContext elementContext = ctx.literalElement(i);

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