使用 LINQ 计算字符串中字母的出现次数

Question

Im trying to implement a piece of code that will return the count of the specified letter in a string. I can do it with a for loop but I find it more elegant of a solution to use LINQ expressions. Here is my code:

public static int CountAs(string countA)
{

    var test = count.Select(x => x == 'a').Count();
        
    return test;

}

Im trying to count how many lower case letter a's exist in the countA parameter. What is wrong with my code?

Thank you in advance!

UPDATE

The method I should be using is the Where method instead of the Select method. Using this fixed my issue:! the function can be rewritten as:

public static int CountAs(string input)
{
   return input.Where(x => x == 'a').Count();
}

Alternatively, you could just use the Count method to directly filter out the desired letter:

public static int CountAs(string input)
{
   return input.Where(x => x == 'a').Count();
}

Thank you everyone that came to the rescue!!

Answer 1

Use .Where instead of .Select . .Where finds items that match your criteria, whereas .Select tells it how to return said items if you need to transform them.

Answer 2

You should use .Count() with a predicate. The .Count() method is used to do data calculation and based on condition (predicate).

.Count()

Returns the number of elements in a sequence.

Meanwhile .Select() is used for data projection / display.

.Select()

Projects each element of a sequence into a new form.

Thus, your output count with .Select() will return the length of your string.

SOLUTION: Calculates the number of lower 'a's only in the string as requested from Post Owner.

public static int CountLowerAs(string input)
{
    return input.Count(x => x == 'a');
}