create-event.cs

[FunctionName("CalculateChangePercent")]
public void CalculateChangePercent(
  [EventGridTrigger] EventGridEvent incomingEvent,
  [Table("stockpricehistory", Connection = "AzureWebJobsStorage")] CloudTable stockPriceHistoryTable,
  [EventGrid(TopicEndpointUri = "TopicUrlSetting", TopicKeySetting = "TopicKeySetting")] ICollector<EventGridEvent> changeEventCollector,
  ILogger logger)
{
  var stockData = ((JObject)incomingEvent.Data).ToObject<StockDataPriceChangeEvent>();
  var selectQuery = new TableQuery<StockDataTableEntity>().Where(
    TableQuery.GenerateFilterCondition(nameof(StockDataTableEntity.PartitionKey), QueryComparisons.Equal, stockData.Symbol)
  );

  var symbolResults = stockPriceHistoryTable.ExecuteQuery(selectQuery).ToList();
  var latestEntry = symbolResults.OrderByDescending(x => x.Timestamp)
    .FirstOrDefault();

  if (latestEntry != null)
  {
    var oldPrice = (decimal) latestEntry.Price;
    var newPrice = stockData.Price;
    var change = Math.Round((oldPrice - newPrice) / oldPrice, 2) * -1;
                
    stockData.Change = change;
  }

  changeEventCollector.Add(new EventGridEvent()
  {
    Id = Guid.NewGuid().ToString(),
    Subject = $"{stockData.Symbol}-price-change", 
    Data = stockData,
    EventType = "EventDrivePoc.Event.StockPriceChange",
    DataVersion = "1.0"
  });
}