vertical table?

test.razor

@if (_data != null)
{
    var dates = _data.Select(x => x.Date).Distinct();

    <table>
        <tr>
            @foreach (var date in dates)
            {
                <th>@date.ToShortDateString()</th>
            }
        </tr>
        @foreach (var date in dates)
        {
            var items = _data.Where(x => x.Date == date);

            // ?
        }
    </table>
}

@code {

    private Datum[]? _data;

    protected override void OnInitialized()
    {
        var list = new List<Datum>();

        for (var i = 0; i < 10; i++)
        {
            list.Add(new Datum { Date = DateTime.Today, Number = i });
        }

        for (var i = 0; i < 10; i++)
        {
            list.Add(new Datum { Date = DateTime.Today.AddDays(1), Number = i });
        }

        for (var i = 0; i < 10; i++)
        {
            list.Add(new Datum { Date = DateTime.Today.AddDays(2), Number = i });
        }

        _data = list.ToArray();
    }

    public class Datum
    {
        public DateTime Date { get; set; }

        public int Number { get; set; }
    }
}