dotnet/machinelearning · error · ArgumentException

Strings.BadColumnCast (formatted with column.DataType, typeo

Error message

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

What it means

GetDateTimeColumn returns the named column as a DateTimeDataFrameColumn or throws ArgumentException(Strings.BadColumnCast, column.DataType, typeof(DateTime)) when the column's type differs. Note this throw omits a paramName, unlike GetPrimitiveColumn.

Source

Thrown at src/Microsoft.Data.Analysis/DataFrameColumnCollection.cs:240

            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)));
        }

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

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

View on GitHub (pinned to 7b76e69cf9)

Solutions

  1. Verify column.DataType == typeof(DateTime) before calling, or catch and convert.
  2. Parse the underlying column into a new DateTimeDataFrameColumn first, add it, then fetch it.
  3. Inspect the actual column kind via pattern matching (is DateTimeDataFrameColumn).

Example fix

// before
var ts = df.Columns.GetDateTimeColumn("ts"); // ts is string column
// after
var tsStr = df.Columns.GetArrowStringColumn("ts");
var ts = new DateTimeDataFrameColumn("ts", tsStr.Select(DateTime.Parse));
df.Columns.Add(ts);
Defensive patterns

Strategy: type-guard

Validate before calling

if (!(df.Columns["ts"] is DateTimeDataFrameColumn))
    throw new InvalidOperationException($"'ts' is {df.Columns["ts"].DataType}, not DateTime");
var ts = df.Columns.GetDateTimeColumn("ts");

Type guard

bool IsDateTimeColumn(DataFrameColumn c) => c is DateTimeDataFrameColumn;

Try / catch

try
{
    var ts = df.Columns.GetDateTimeColumn(name);
}
catch (ArgumentException)
{
    // convert/parse the actual column type into DateTimeDataFrameColumn
}

Prevention

When it happens

Trigger: df.Columns.GetDateTimeColumn("ts") where the column is e.g. a string or PrimitiveDataFrameColumn, not DateTimeDataFrameColumn.

Common situations: Date columns parsed as strings from CSV, timestamp columns stored as long (unix epoch), timezone columns of differing storage types.

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/9b23b89545b536a0. Report an issue: GitHub.