dotnet/machinelearning · error · ArgumentException

Strings.BadColumnCast (formatted with column.DataType, typeo

Error message

Strings.BadColumnCast (formatted with column.DataType, typeof(Boolean))

What it means

GetBooleanColumn returns the named column as a BooleanDataFrameColumn or throws ArgumentException(Strings.BadColumnCast, column.DataType, typeof(Boolean)) when the underlying column is not boolean (e.g. a byte or int column).

Source

Thrown at src/Microsoft.Data.Analysis/DataFrameColumnCollection.cs:291

            throw new ArgumentException(string.Format(Strings.BadColumnCast, column.DataType, typeof(string)));
        }

        /// <summary>
        /// Gets the <see cref="BooleanDataFrameColumn"/> with the specified <paramref name="name"/>.
        /// </summary>
        /// <param name="name">The name of the column</param>
        /// <returns><see cref="BooleanDataFrameColumn"/>.</returns>
        /// <exception cref="ArgumentException">A column named <paramref name="name"/> cannot be found, or if the column's type doesn't match.</exception>
        public BooleanDataFrameColumn GetBooleanColumn(string name)
        {
            DataFrameColumn column = this[name];
            if (column is BooleanDataFrameColumn ret)
            {
                return ret;
            }

            throw new ArgumentException(string.Format(Strings.BadColumnCast, column.DataType, typeof(Boolean)));
        }

        /// <summary>
        /// Gets the <see cref="ByteDataFrameColumn"/> with the specified <paramref name="name"/> and attempts to return it as an <see cref="ByteDataFrameColumn"/>. If <see cref="DataFrameColumn.DataType"/> is not of type <see cref="Byte"/>, an exception is thrown.
        /// </summary>
        /// <param name="name">The name of the column</param>
        /// <returns><see cref="ByteDataFrameColumn"/>.</returns>
        /// <exception cref="ArgumentException">A column named <paramref name="name"/> cannot be found, or if the column's type doesn't match.</exception>
        public ByteDataFrameColumn GetByteColumn(string name)
        {
            DataFrameColumn column = this[name];
            if (column is ByteDataFrameColumn ret)
            {
                return ret;
            }

            throw new ArgumentException(string.Format(Strings.BadColumnCast, column.DataType, typeof(Byte)));
        }

View on GitHub (pinned to 7b76e69cf9)

Solutions

Check df.Columns["flag"].DataType == typeof(bool) before calling.
Convert the numeric/string column to a BooleanDataFrameColumn and add it to the DataFrame first.
Catch the ArgumentException and fall back to a conversion path.

Example fix

// before
var flag = df.Columns.GetBooleanColumn("IsActive"); // stored as byte
// after
var bytes = df.Columns.GetPrimitiveColumn<byte>("IsActive");
var flag = new BooleanDataFrameColumn("IsActive", bytes.Select(b => b != 0));
df.Columns.Add(flag);

Defensive patterns

Strategy: type-guard

Validate before calling

if (df.Columns["IsActive"].DataType != typeof(bool))
    throw new InvalidOperationException($"'IsActive' is {df.Columns["IsActive"].DataType}, expected bool");
var flag = df.Columns.GetBooleanColumn("IsActive");

Type guard

bool IsBooleanColumn(DataFrameColumn c) => c is BooleanDataFrameColumn;

Try / catch

try
{
    var flag = df.Columns.GetBooleanColumn(name);
}
catch (ArgumentException)
{
    // convert byte/int/string column to BooleanDataFrameColumn
}

Prevention

Verify boolean flags survive ingestion as bool (CSV 'True/False', DB bit).
Convert 0/1 or 'true/false' encodings to BooleanDataFrameColumn at load time.
Check DataType before every typed getter.

When it happens

Trigger: df.Columns.GetBooleanColumn("flag") where the column stores byte/int/char values instead of BooleanDataFrameColumn.

Common situations: CSV 'true/false' parsed as string or 0/1 parsed as numeric, flags imported from databases as smallint, nullable boolean data stored as byte columns.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of dotnet/machinelearning@7b76e69cf9 (2026-09-11). Data as JSON: /api/errors/ad6ce8cd8457e616. Report an issue: GitHub.