How do I get first element of each array via Linq C#

Question

I'm very new to Linq and having a problem with this code:

double[] values;
private List<double[]> valueList = new List<double[]>();
void AddNewValues(double d1, double d2, double d3)
{
   values[0] = d1;
   values[1] = d1;
   values[2] = d1;
   valueList.Add(values);
}

void GetAllFirstValues()
{
   var test = valueList.Where(s => s == typeof(double[0]));
}

How to get the first item of each array inside the list?

Is that even possible? Is Linq here a proper way to do that or is there a more clever solution?

var test = valueList.Where(s => s == typeof(double[0])).FirstOrDefault(); — Syntax Error
– Syntax Error, Commented Feb 23, 2018 at 8:39
Why typeof(double[0]) and not s.First()? Why you use typeof at all? Use valueList.Select(s => s.First()) — Tim Schmelter
– Tim Schmelter, Commented Feb 23, 2018 at 8:41
Aside from the fact typeof(double[0]) is not valid syntax, the check s == typeof(double[]) will never be true in the above example. s is an double array value, while typeof(double[]) would return the Type. If you want to check if it is a double array you'll need s.GetType() == typeof(double[]) or with pattern matching s is double[]. However, this is unneeded in your code as the List is typed to a double[]. — RMH
– RMH, Commented Feb 23, 2018 at 8:56
lots of problems/weirdness with your setup code that should be fixed before anybody tries to answer. 1. you haven't initialized the values array, so the values[0] = d1, etc. statements will all throw exceptions. 2. You are assigning the value of d1 to the array elements all three times, ignoring d2 and d3 (probably not your intention). It would probably help you to first add several calls to AddNewValues() so you can see what's wrong with your AddNewValues() method. — Richard II
– Richard II, Commented Feb 12, 2019 at 14:45

Johnny · Accepted Answer · 2019-07-05 12:59:48Z

10

This should be System.Linq, you don't need to check for type. It will select first or default if array is empty and return it.

IEnumerable<double> d =  l.Select(array => array.FirstOrDefault())

or, if you want to filter only non empty arrays:

IEnumerable<double> d = l.Where(array => array.Any()).Select(array => array.First());

Be aware that array also can be null, so you can even filter that out within the Where clause.

edited Jul 5, 2019 at 12:59

answered Feb 23, 2018 at 8:42

Johnny

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