Check null or empty IEnumerable in C#

Question

What is the best way to check null or empty for IEnumerable<double> in C#?

What I have tried so far is

return returnList != null && returnList.Any();

but I get a message that this expression will always return true.

Full method:

public double ArithmeticMean(IEnumerable<double> ReturnsList, bool IsMonthly)
{
    var returnList = ReturnsList.Mean();

    if (IsMonthly)
    {
        return returnList;
    }
    else
    {
        return returnList * Math.Pow(12, 0.5);
    }
}

Please provide a [mcve]. We don't have enough information to help you at the moment. — Jon Skeet, Apr 05 '19 at 15:58
We don't have enough information, but at a guess I'm assuming you are using Resharper and it's telling you that `returnList` is not null so you have a redundant check. — DavidG, Apr 05 '19 at 16:00
if returnList is a simple IEnumerable then it should work. Show us the code before that. — Steve Todd, Apr 05 '19 at 16:00
Is `.Mean()` and extension method? Can you show the definition? — Equalsk, Apr 05 '19 at 16:19
But before that i need to check if ReturnsList is null or empty — Tom, Apr 05 '19 at 16:20
from the shown code we can't help you much. From my perspective null or empty are both valid cases. Who is giving that message? — MakePeaceGreatAgain, Apr 05 '19 at 16:27
It looks to me like returnList is just one double, not a list of anything. — Mike, Apr 05 '19 at 16:29
I wonder how `returnList.Any()` should ever compile, as returnList seems to be a single double. You surely want to check for `returnsList` with s in the middle — MakePeaceGreatAgain, Apr 05 '19 at 16:35

score 0 · Answer 1 · answered Apr 05 '19 at 16:31

0

The Math.NET documentation says of the Mean() function:

https://numerics.mathdotnet.com/api/MathNet.Numerics.Statistics/Statistics.htm#Mean

Evaluates the sample mean, an estimate of the population mean. Returns NaN if data is empty or if any entry is NaN.

Neither the mean or Double.NaN are null, so returnList is never null, making the check for this redundant as proposed by ReSharper.

answered Apr 05 '19 at 16:31

Equalsk

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The returnrnlist is an array of double values passed to the method. There could be a possibility that the caller of the method might not pass the returnlist in that case you would be doing mean of nothing – Tom Apr 06 '19 at 14:03

Check null or empty IEnumerable in C#

1 Answers1