How to elegantly assign values in function of number range?

Question

I am searching of an elegant way to assign values in function of a number belonging to a specific range.

For example, having the number X, the elegant way would return:

'a' - if X is between 0 and 1000
'b' - if X is between 1000 and 1500
and so on (but a fixed number of defined intervals)

By elegant I mean something more appealing than

if ((x => interval_1) && (x < interval_2))
    class_of_x = 'a';
else if ((x => interval_2) && (x < interval_3))
    class_of_x = 'b';
...

or

if(Enumerable.Range(interval_1, interval_2).Contains(x))
    class_of_x = 'a';
else if(Enumerable.Range(interval_2 + 1, interval_3).Contains(x))
    class_of_x = 'b';
...

I hate seeing so many IFs. Also, the interval values can be stored in a collection (maybe this would help me eliminate the ISs?), not necessary as interval_1, interval_2 and so on.

Somewhat inspired by this question How to elegantly check if a number is within a range? which came out while looking for a solution for the problem described above.

does the next interval always start from the end of the previous? — Sayse, Aug 14 '13 at 15:11

score 1 · Answer 1 · answered Aug 14 '13 at 15:15

1

If my comment is correct then your first if statement has a lot of unnecessary checks, if its not less than interval 2 then it must be greater than or equal to, therefore:

if((x => i1) && (x < i2))
else if(x < i3)
else if(x < i4)...

When a "true" argument is found then the rest of the if statement is irrelevant, as long as your conditions are in order this should suit your needs

answered Aug 14 '13 at 15:15

Sayse

42,633
14
77
146

Seems I have overlooked this for sure. :D Less code, but still a lot of IFs. – Coral Doe Aug 14 '13 at 15:17
Other than this there isn't really a way to avoid lots of if statements, you could always do some combination of math.round and a switch statement I guess but thats not really achieving much – Sayse Aug 14 '13 at 15:21

score 1 · Accepted Answer · answered Aug 14 '13 at 15:17

You can create extention method:

public static class IntExtensions
{
    // min inclusive, max exclusive
    public static bool IsBetween(this int source, int min, int max)
    {
        return source >= min && source < max
    }
}

and then

// Item1 = min, Item2 = max, Item3 = character class
IList<Tuple<int, int, char>> ranges = new List<Tuple<int, int, char>>();
// init your ranges here
int num = 1;
// assuming that there certainly is a range which fits num,
// otherwise use "OrDefault"
// it may be good to create wrapper for Tuple, 
// or create separate class for your data
char characterClass = ranges.
                        First(i => num.IsBetween(i.Item1, i.Item2)).Item3;

Matthew Watson · Answer 3 · 2013-08-14T15:27:43.483

Firstly, define a little class to hold the inclusive maximum value, and the corresponding value to use for that band:

sealed class Band
{
    public int  InclusiveMax;
    public char Value;
}

Then declare an array of Band which specifies the value to use for each band and loop to find the corresponding band value for any input:

public char GetSetting(int input)
{
    var bands = new[]
    {
        new Band {InclusiveMax = 1000, Value = 'a'},
        new Band {InclusiveMax = 1500, Value = 'b'},
        new Band {InclusiveMax = 3000, Value = 'c'}
    };

    char maxSetting = 'd';

    foreach (var band in bands)
        if (input <= band.InclusiveMax)
            return band.Value;

    return maxSetting;
}

Note: In real code, you would wrap all this into a class which initialises the bands array only once, and not every single time it's called (as it is in the code above).

score 1 · Answer 4 · answered Aug 14 '13 at 15:25

1

Create an Interval class and use LINQ:

public class Interval
{
    public string TheValue { get; set; }
    public int Start { get; set; }
    public int End { get; set; }

    public bool InRange(int x)
    {
        return x >= this.Start && x <= this.End;
    }
}

public void MyMethod()
{
    var intervals = new List<Interval>();

    // Add them here...

    var x = 3213;
    var correctOne = intervals.FirstOrDefault(i => i.InRange(x));

    Console.WriteLine(correctOne.TheValue);
}

answered Aug 14 '13 at 15:25

Patrik Westerlund

466
3
9

1

given the inputs specified in the question, your own code would cause an NRE on the bottom line – Sayse Aug 14 '13 at 15:27
1

And given this is a very simple example of a pattern and not a complete code piece that should simply be copy-pasted, I didn't add an if-statement. – Patrik Westerlund Aug 15 '13 at 06:46
See my alternative version with the use of Linq's static Enumerable.Range() method below... – C. Sederqvist Nov 08 '13 at 09:15

score 0 · Answer 5 · answered Nov 08 '13 at 09:07

Here you could also use the static System.Linq.Enumerable's Range() method that implements

IEnumerable<T>

with the Contains() method (again from System.Linq.Enumerable), to do something like:

var num = 254;
if(Enumerable.Range(100,300).Contains(num)) { ...your logic here; }

This looks more elegant in my eyes at least.

How to elegantly assign values in function of number range?

5 Answers5