dotnet/machinelearning · error · ArgumentException

Strings.BadColumnCast (formatted with column.DataType, typeo

Error message

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

What it means

GetPrimitiveColumn<T> fetches the column by name and throws ArgumentException(Strings.BadColumnCast, column.DataType, typeof(T)) if it is not a PrimitiveDataFrameColumn<T>. This guards against invalid type-based column casts.

Source

Thrown at src/Microsoft.Data.Analysis/DataFrameColumnCollection.cs:223

            }
        }

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

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

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

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

View on GitHub (pinned to 7b76e69cf9)

Solutions

Check column.DataType first and request the matching T (e.g. use GetPrimitiveColumn<long> for Int64).
Inspect df.Columns[name].DataType (or df.Schema) and branch on the actual type.
Convert the column (Clone/Cast) to the desired primitive type before retrieval.

Example fix

// before
var col = df.Columns.GetPrimitiveColumn<int>(\"Age\"); // Age is Int64
// after
if (df.Columns["Age"].DataType == typeof(long))
    var col = df.Columns.GetPrimitiveColumn<long>("Age");

Defensive patterns

Strategy: type-guard

Validate before calling

var type = df.Columns["Age"].DataType;
var col = type == typeof(int)
    ? df.Columns.GetPrimitiveColumn<int>("Age")
    : throw new InvalidOperationException($"'Age' is {type}, expected int");

Type guard

bool IsPrimitive<T>(DataFrameColumn c) => c is PrimitiveDataFrameColumn<T>;

Try / catch

try
{
    var col = df.Columns.GetPrimitiveColumn<int>(name);
}
catch (ArgumentException ex) when (ex.ParamName == "T")
{
    // inspect column.DataType and retry with matching T
}

Prevention

Inspect column.DataType (or df.Schema) before typed getters.
Account for loader type inference (int columns often arrive as long/double).
Prefer pattern matching (is PrimitiveDataFrameColumn<T>) over blind casts.

When it happens

Trigger: df.Columns.GetPrimitiveColumn<int>("name") where the stored column is not PrimitiveDataFrameColumn<int> (wrong primitive type, or a string/datetime/arrow column).

Common situations: CSV inference giving float where int was expected, schema drift across files, assuming int columns that contain nulls are Int32 instead of Nullable Int64 defaults.

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/6c01dcae0fe135a3. Report an issue: GitHub.