apache/beam · error

Unexpected number type

Error message

Unexpected number type: %v

What it means

The stats Max transform selects a combine function based on the element type name at graph construction; only numeric types (ints, uints, float32/64, etc.) are supported. If the PCollection's type is any other kind, findMaxFn panics because maximum of a non-number is undefined here.

Solutions

1. Ensure the input PCollection to stats.Max has a concrete numeric element type (int..int64, uint..uint64, float32, float64).
2. Convert non-numeric data to a number before maximizing (e.g. parse or map to float64).
3. Check upstream type inference: use beam.Encoding / explicit typed ParDo so the type isn't interface{} or string.
4. Use a custom combinefn for non-numeric orderable types instead of stats.Max.

Example fix

// before
max := stats.Max(s, strs) // strs is PCollection<string>
// after
nums := beam.ParDo(s, parseNum, strs) // map string -> float64 first
max := stats.Max(s, nums)

func isMaxSupported(v any) bool {
	switch v.(type) {
	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64:
		return true
	}
	return false
}
// call before stats.Max: if !isMaxSupported(firstElem) { convert or use custom combine }

When it happens

Trigger: Using stats.Max (via findMaxFn) on a PCollection whose coder type string is not one of the handled numeric types — e.g. strings, structs, or custom types — during pipeline construction/ProcessElement setup.

Common situations: Accidentally feeding string or boolean collections into Max, type inference resolving to 'any'/interface after a refactor, or applying Max to encoded byte slices.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• pubsubio.Write only accepts PCollections of
• type must be a non-complex number
• Unexpected number type
• Unexpected number type
• AfterProcessingTime trigger set without a delay or…

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/f970e368237550a8. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/transforms/stats/max_switch.go:52

		return maxInt32Fn
	case "int64":
		return maxInt64Fn
	case "uint":
		return maxUintFn
	case "uint8":
		return maxUint8Fn
	case "uint16":
		return maxUint16Fn
	case "uint32":
		return maxUint32Fn
	case "uint64":
		return maxUint64Fn
	case "float32":
		return maxFloat32Fn
	case "float64":
		return maxFloat64Fn
	default:
		panic(fmt.Sprintf("Unexpected number type: %v", t))
	}
}

func maxIntFn(x, y int) int {
	if x > y {
		return x
	}
	return y
}

func maxInt8Fn(x, y int8) int8 {
	if x > y {
		return x
	}
	return y
}

func maxInt16Fn(x, y int16) int16 {

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