You can check elements in a list or an array using a list pattern.
Consider the following excerpt from a text file containing bank transactions:
04-01-2020, DEPOSIT, Initial deposit, 2250.00
04-15-2020, DEPOSIT, Refund, 125.65
04-18-2020, DEPOSIT, Paycheck, 825.65
04-22-2020, WITHDRAWAL, Debit, Groceries, 255.73
05-01-2020, WITHDRAWAL, #1102, Rent, apt, 2100.00
05-02-2020, INTEREST, 0.65
05-07-2020, WITHDRAWAL, Debit, Movies, 12.57
04-15-2020, FEE, 5.55
A list pattern that includes the discard pattern, constant pattern, and var pattern to capture the value processes data in this format:
decimal balance = 0m;
foreach (string[] transaction in ReadRecords())
{
balance += transaction switch
{
[_, "DEPOSIT", _, var amount] => decimal.Parse(amount),
[_, "WITHDRAWAL", .., var amount] => -decimal.Parse(amount),
[_, "INTEREST", var amount] => decimal.Parse(amount),
[_, "FEE", var fee] => -decimal.Parse(fee),
_ => throw new InvalidOperationException($"Record {string.Join(", ", transaction)} is not in the expected format!"),
};
Console.WriteLine($"Record: {string.Join(", ", transaction)}, New balance: {balance:C}");
}
The preceding example takes a string array, where each element is one field in the row. The switch expression keys on the second field, which determines the kind of transaction, and the number of remaining columns. Each row ensures the data is in the correct format. The discard pattern (_) skips the first field, with the date of the transaction. The second field matches the type of transaction. Remaining element matches skip to the field with the amount. The final match uses the var pattern to capture the string representation of the amount. The expression calculates the amount to add or subtract from the balance.
Source: https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/functional/pattern-matching