Return List

Question

I have a method:

public List<AxeResult> LoadAxes(string kilometriczone, string axe)
{
    IEnumerable<AxeResult> allAxes = PullAxes();
    var findAxes = allAxes.Select(a => a.KilometricZone.StartsWith(kilometriczone) || a.KilometricZone.StartsWith(axe));

    return findAxes.Cast<AxeResult>().ToList();
}

I have this error:

IEnumerable<bool> does not contain a definition for ToList and the best extension method overload Enumerable.ToList<AxeResult> ( IEnumerable<AxeResult>) requires a receptor type IEnumerable<AxeResult>

I want to return a List of AxeResult after the search operation.

You use `Select` with `StartsWith`, which returns a `bool`. Maybe you want to use a where statement instead? — wimh, Apr 15 '16 at 11:47
That error message is odd. I would have expected a run time `InvalidCastException` about not being able to cast `bool` to `AxeResult`. — juharr, Apr 15 '16 at 12:00

score 7 · Accepted Answer · answered Apr 15 '16 at 11:48

What you want is to filter the collection. That's what Enumerable.Where is for:

public List<AxeResult> LoadAxes(string kilometriczone, string axe)
{
    return PullAxes()
        .Where(a => a.KilometricZone.StartsWith(kilometriczone) || 
                    a.KilometricZone.StartsWith(axe))
        .ToList();
}

score 2 · Answer 2 · edited May 23 '17 at 12:23

2

Some explanation in addition to the given answers:

Where() method acts like a filter and returns a subset of the same set

Select() method makes projection and returns new set

There is comprehensive explanation about the diffrence between .Select() and Where() methods here.

edited May 23 '17 at 12:23

Community

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answered Apr 15 '16 at 12:11

Tanya Petkova

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2 Answers2