Best way to find values in range

Question

I have a collection of values:

[0-20] = 1
[21-30] = 2
[31-40] = 3 etc.

I expect input from users in the for of [44] for example. What would be the most eloquent way to determine in which item the value falls?

I can write a switch statement to match a case > < or an if...statement but neither of these in my opinion is eloquent enough.

Update

I'm looking for a neat and tidy way of finding the range in which my user's input fall, using something like LAMDBA for example:

List<int>().Find(x => x.WithinRange(range))

Or something like that.

`if` statements are fine: simple, effective and understandable. — ken2k, Feb 02 '12 at 14:27
Do you need speed? If so, then a massive dictionary would be the fastest way, anyhow I do not see a good reason to waste so much memory and make code harder to read for such a little performance gain — Yurii Hohan, Feb 02 '12 at 14:29
Possible duplicate of: http://stackoverflow.com/questions/1447635/linq-between-operator — CodingGorilla, Feb 02 '12 at 14:31
Is this meant to follow a pattern of going up in 10s where you say "etc."? — weston, Feb 02 '12 at 14:54

hunter · Answer 1 · 2012-02-02T14:44:57.243

4

Something like this as an extension:

public static int WithinRange(this int value)
{
    if (value < 0) return 0;
    if (value < 21) return 1;
    return (value - 1) / 10;
}

without if statements

public static int WithinRange(this int value)
{
    return (value < 0) ? 0 
        : (value < 21) ? 1 
        : (value - 1) / 10;
}

usage:

collection.Find(x => x.WithinRange(range))

edited Feb 02 '12 at 14:44

answered Feb 02 '12 at 14:27

hunter

62,308
19
113
113

something like this, but without using IF statements :$ – JadedEric Feb 02 '12 at 14:28
nothing wrong with if statements, i was just curious about other ways of finding a value within a given min / max range – JadedEric Feb 02 '12 at 14:31
not sure if you can avoid `if` statements since your first case of `0-20` doesn't fit the the other patterns – hunter Feb 02 '12 at 14:34

score 4 · Answer 2 · answered Feb 02 '12 at 14:32

If your ranges are consecutive, as in your example (i.e. there are no gaps), you can store their endpoints in an array, like this:

var endpoints = new[] {20, 30, 40, 60, 90};

Note that the endpoints are sorted. You can now use a binary search method to find the insertion point of 44 in this array, which is 3, will be returned (binary search will return bitwise complement of 3; you'd need to apply ~ to get the actual value).

score 4 · Answer 3 · answered Feb 02 '12 at 14:32

4

There you go:

int GetRange(int value) 
{ 
    return (value > 30) ? 3 :
           (value > 20) ? 2 :
           (value > 0)  ? 1 :
           0;
}

No ifs!

answered Feb 02 '12 at 14:32

weston

54,145
21
145
203

score 2 · Answer 4 · answered Feb 02 '12 at 14:31

Just loop over the ranges and see if the value falls within the range...

var ranges = new[]
{
    Tuple.Create(0, 20),
    Tuple.Create(21, 30),
    Tuple.Create(31, 40),
    Tuple.Create(41, 50),
    // ...
};
var number = 44;
for (int i = 0; i < ranges.Length; i++)
{
    var range = ranges[i];
    if (number >= range.Item1 && number <= range.Item2)
    {
        var theIndex = i + 1;
        // do something with theIndex
    }
}

score 1 · Answer 5 · answered Feb 02 '12 at 14:31

1

You could just manipulate the inputs:

int input = //Whatever the input is
int index = (input-1)/10;

Assuming integer input, and that your array is indexed as indicated.

answered Feb 02 '12 at 14:31

NominSim

8,447
3
28
38

lalibi · Answer 6 · 2012-02-02T15:18:31.843

UPDATE: I know this is an overkill but it might give you some ideas. As I undestand, you already know how to solve this problem, but you are just looking for a "prettier" solution:

public class Range
{
    public int Left { get; set; }   
    public int Right { get; set; }
    public string Title { get; set; }

    public Range(int left, int right, string title) { Left = left; Right = right; Title = title; }

    public bool Contains(int x) { return Left <= x && x <= Right; }
}

void Main()
{
    var x = 15;

    var ranges = new[] {
        new Range(0, 10, "A"),
        new Range(11, 20, "B")
    };

    var foo = ranges.Where(r => r.Contains(x)).Single();

    Console.Write(foo.Title);
}

My previous suggestion: For statement is ok but I prefer LINQ :)

var x = 15;

var ranges = new[] { Tuple.Create(0, 10), Tuple.Create(11, 20) };
var range = ranges.Where(r => r.Item1 <= x && r.Item2 >= x );

Console.Write(range.Item1);
Console.Write(range.Item2);

Tuples are 4.0 specific, should have mentioned I'm on a 3.5 project. But thanks for all the feedback guys, really appreciate the expertise on this forum. — JadedEric, Feb 02 '12 at 14:40

score 0 · Answer 7 · answered Feb 02 '12 at 14:54

Less efficient .NET 3.5 alternative variation of @Jeff Mercado's answer:

var ranges = new[]
{
    Enumerable.Range(0, 20),
    Enumerable.Range(21, 30),
    Enumerable.Range(31, 40),
    Enumerable.Range(41, 50),
    // ...
};
var number = 44;
for (int i = 0; i < ranges.Length; i++)
{
    var range = ranges[i];
    if (range.Contains(number))
    {
        var theIndex = i + 1;
        // do something with theIndex
    }
}

Best way to find values in range

7 Answers7