Functional way to check if array of numbers is sequential

Question

Let's say that an array is sequential when each successful element has the value of previous element + 1. Suppose I have an array of numbers like {5,6,7,8} (sequential) or {1,2,5} (not sequential).

Is there a nice functional way to check if the array is sequential? I can do it with the following code:

bool IsSequential(int[] array)
{
    for (int i = 1; i < array.Length; i++)
       if (array[i] != array[i - 1] + 1)
            return false;
    return true;
}

I'm trying to determine if a poker hand is straight.

How do you deal with the ace? If its value is 1, you can't use this method to detect an ace-high straight. — Gabe
– Gabe, Commented Aug 14, 2013 at 7:06

Kamil Budziewski · Accepted Answer · 2013-08-14 06:55:42Z

22

Try this one:

    bool IsSequential(int[] array)
    {
        return array.Zip(array.Skip(1), (a, b) => (a + 1) == b).All(x => x);
    }

answered Aug 14, 2013 at 6:55

Kamil Budziewski

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3 Comments

Gabe Over a year ago

@AlexeiLevenkov: If you don't use Skip, you're just comparing elements with themselves, which of course will always be equal.

Alan Schapira Over a year ago

Just to add, this will not work if the array of ints is not in order. e.g. this would work with [4,5,6] but not with [5,4,6]. You can just use array.OrderBy(a => a).Zip(array.Skip(1), (a, b) => (a + 1) == b).All(x => x); to get the latter to work.

Aaron Over a year ago

For this to also work for decreasing sequential arrays, use

return array.Zip(array.Skip(1), (a, b) => (a + 1) == b).All(x => x) || array.Zip(array.Skip(1), (a, b) => (a - 1) == b).All(x => x);

Serge · Accepted Answer · 2013-08-19 07:16:59Z

8

I don't know if it's really an improvement/nicer but you could use Range.

ENumerable.Range(0, myArray.Length).Any(i => myArray[i] != myArray[0] + i)

This returns true if the array doesn't contain sequential number.

edited Aug 19, 2013 at 7:16

answered Aug 14, 2013 at 6:56

Serge

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1 Comment

WynandB Over a year ago

Nice, although if we want to check if an array is sequential: Enumerable.Range(0, myArray.Length).All(i => myArray[i] == myArray[0] + i)

JDunkerley · Accepted Answer · 2013-08-14 07:02:10Z

2

Using Linq:

    public static bool IsSequential(int[] a)
    {
        return Enumerable.Range(1, a.Length - 1).All(i => a[i] - 1 == a[i - 1]);
    }

answered Aug 14, 2013 at 7:02

JDunkerley

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Comments

Ehsan · Accepted Answer · 2013-08-14 07:02:42Z

2

This should do the trick, for all sequential, non sequential data. A complete example with sample input. Tested and works fine

var list = new List<int>(new[] { 7, 6, 5, 4, 3,9});
int minValue = list.Min();
int maxValue = list.Count;
List<int> test =  Enumerable.Range(minValue, maxValue).ToList();
var result = Enumerable.Range(minValue, maxValue).Except(list);
if (result.ToList().Count == 0)
{
  Console.WriteLine("numbers are in sequence");
}
else
{               
   Console.WriteLine("Numbers are not in sequence");
 }

answered Aug 14, 2013 at 7:02

Ehsan

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Comments

AKD · Accepted Answer · 2013-08-14 06:58:02Z

1

var result = Enumerable.Range(array[0], array[array.Length-1]).Except(array.ToList());

answered Aug 14, 2013 at 6:58

AKD

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Comments

Community · Accepted Answer · 2017-05-23 12:33:15Z

1

Same as: make sure array is sequential in C#

Answer there:

if you're sure that the array is sorted and has no duplicates, you can just check:

array[array.Length - 1] == array[0] + array.Length - 1

edited May 23, 2017 at 12:33

CommunityBot

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answered Aug 14, 2013 at 6:57

sara

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2 Comments

Serge Over a year ago

That's wrong, with this you can't know anything about the other elements than first and last.

sara Over a year ago

@Serge that's why specified: if you're sure that the array is sorted and has no duplicates. If so - the answer is correct. Think why!

Jeffrey Zhang · Accepted Answer · 2024-09-03 08:50:56Z

1

Try this one, I think it is most simple:

nums.Select((n, i) => n - i).Distinct().Count() == 1

answered Sep 3, 2024 at 8:50

Jeffrey Zhang

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Comments

Asmussen · Accepted Answer · 2017-09-27 12:53:35Z

0

First sort the array, remove N of a kind (e.g. pairs) using distinct() and If the array length is always == to 5 All you need to do is if((array[4] - array[0]) == 4) return true.

It gets more complicated if its texas holdem or if you need to account for both an ace high and ace low straight.

answered Sep 27, 2017 at 12:53

Asmussen

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