pola-rs/polars · error

Comparison of UnionArrays is not yet supported

Error message

Comparison of UnionArrays is not yet supported

What it means

unimplemented!/todo!() arm in the comparison kernel dispatch: comparing arrays of the matched physical type (e.g. UnionArray or MonthDayMillis interval) has no kernel in this build. Signals unsupported functionality for that dtype in comparisons, not invalid user input.

Source

Thrown at crates/polars-compute/src/comparisons/array.rs:202

            PH::Primitive(PR::MonthDayMillis) => unimplemented!(),

            #[cfg(feature = "dtype-array")]
            PH::FixedSizeList => call_binary!(arrow::array::FixedSizeListArray),
            #[cfg(not(feature = "dtype-array"))]
            PH::FixedSizeList => todo!(
                "Comparison of FixedSizeListArray is not supported without dtype-array feature"
            ),

            PH::Null => call_binary!(NullArray),
            PH::FixedSizeBinary => call_binary!(FixedSizeBinaryArray),
            PH::Binary => call_binary!(BinaryArray<i32>),
            PH::LargeBinary => call_binary!(BinaryArray<i64>),
            PH::Utf8 => call_binary!(Utf8Array<i32>),
            PH::LargeUtf8 => call_binary!(Utf8Array<i64>),
            PH::List => call_binary!(ListArray<i32>),
            PH::LargeList => call_binary!(ListArray<i64>),
            PH::Struct => call_binary!(StructArray),
            PH::Union => todo!("Comparison of UnionArrays is not yet supported"),
            PH::Map => todo!("Comparison of MapArrays is not yet supported"),
            PH::Dictionary(I::Int8) => call_binary!(DictionaryArray<i8>),
            PH::Dictionary(I::Int16) => call_binary!(DictionaryArray<i16>),
            PH::Dictionary(I::Int32) => call_binary!(DictionaryArray<i32>),
            PH::Dictionary(I::Int64) => call_binary!(DictionaryArray<i64>),
            PH::Dictionary(I::Int128) => call_binary!(DictionaryArray<i128>),
            PH::Dictionary(I::UInt8) => call_binary!(DictionaryArray<u8>),
            PH::Dictionary(I::UInt16) => call_binary!(DictionaryArray<u16>),
            PH::Dictionary(I::UInt32) => call_binary!(DictionaryArray<u32>),
            PH::Dictionary(I::UInt64) => call_binary!(DictionaryArray<u64>),
            PH::Dictionary(I::UInt128) => call_binary!(DictionaryArray<u128>),
        }
    }};
}

fn array_fsl_tot_eq_missing_kernel(
    values: &dyn Array,
    scalar: &dyn Array,

View on GitHub (pinned to 9b5d73fd00)

Solutions

  1. Comparison of UnionArrays is not supported; convert the union to a concrete type (e.g. via casting or flattening) before comparing.
  2. Compare the union's child arrays individually instead of the union array itself.
Defensive patterns

Strategy: fallback

When it happens

Trigger: This panic/expect fires when execution reaches an unguarded state described by: "Comparison of UnionArrays is not yet supported". Typical triggers: unsupported dtype or feature-gated code path reached at runtime, invalid user input or environment variable value, calling API methods in the wrong order or on mismatched types, or data (lengths, offsets, ranges) violating the function's preconditions.

Common situations: Encountered when input data or configuration does not meet the preconditions of the throwing code path ("Comparison of UnionArrays is not yet supported"). Common cases: missing Cargo feature flags, mismatched dtypes/lengths between arrays or series, out-of-range temporal values, malformed environment variables, or operations on unsupported/complex nested types.

AI-assisted analysis of pola-rs/polars@9b5d73fd00 (2026-08-19). Data as JSON: /api/errors/07d6275cef2e7135. Report an issue: GitHub.