Finding closest match in collection of numbers

Question

So I got asked today what was the best way to find the closes match within a collection.

For example, you've got an array like this:

1, 3, 8, 10, 13, ...

What number is closest to 4?

Collection is numerical, unordered and can be anything. Same with the number to match.

Lets see what we can come up with, from the various languages of choice.

Answer 1

EDITED = in the for loop

int Closest(int val, int[] arr)
{
    int index = 0;
    for (int i = 0; i < arr.Length; i++)
     if (Math.Abs(arr[i] - val) < Math.Abs(arr[index] - val))
      index = i;
    return arr[index];
}

Answer 2

Assuming that the values start in a table called T with a column called N, and we are looking for the value 4 then in Oracle SQL it takes 59 characters:

select*from(select*from t order by abs(n-4))where rownum=1

I've used select * to reduce the whitespace requirements.

Answer 3

My attempt in python:

def closest(target, collection) :
    return min((abs(target - i), i) for i in collection)[1]

Answer 4

int numberToMatch = 4;

var closestMatches = new List<int>();
closestMatches.Add(arr[0]); // closest tentatively

int closestDifference = Math.Abs(numberToMatch - arr[0]);


for(int i = 1; i < arr.Length; i++)
{
 int difference = Math.Abs(numberToMatch - arr[i]);
 if (difference < closestDifference)
 {
  closestMatches.Clear();
  closestMatches.Add(arr[i]);
  closestDifference = difference;
 }
 else if (difference == closestDifference)
 {  
  closestMatches.Add(arr[i]);
 }
}


Console.WriteLine("Closest Matches");
foreach(int x in closestMatches) Console.WriteLine("{0}", x);

Answer 5

Some of you don't seem to be reading that the list is unordered (although with the example as it is I can understand your confusion). In Java:

public int closest(int needle, int haystack[]) { // yes i've been doing PHP lately
  assert haystack != null;
  assert haystack.length; > 0;
  int ret = haystack[0];
  int diff = Math.abs(ret - needle);
  for (int i=1; i<haystack.length; i++) {
    if (ret != haystack[i]) {
      int newdiff = Math.abs(haystack[i] - needle);
      if (newdiff < diff) {
        ret = haystack[i];
        diff = newdiff;
      }
    }
  }
  return ret;
}

Not exactly terse but hey its Java.

Answer 6

Haskell entry (tested):

import Data.List

near4 = head . sortBy (\n1 n2 -> abs (n1-4) `compare` abs (n2-4))

Sorts the list by putting numbers closer to 4 near the the front. head takes the first element (closest to 4).

Answer 7

Ruby

def c(r,t)
r.sort{|a,b|(a-t).abs<=>(b-t).abs}[0]
end

Not the most efficient method, but pretty short.

Answer 8

returns only one number:

var arr = new int[] { 1, 3, 8, 10, 13 };
int numToMatch = 4;
Console.WriteLine("{0}", 
     arr.Select(n => new{n, diff = Math.Abs(numToMatch - n) }).OrderBy(x => x.diff).ElementAt(0).n);

Answer 9

PostgreSQL:

select n from tbl order by abs(4 - n) limit 1

Answer 10

returns only one number:

var arr = new int[] { 1, 3, 8, 10, 13 };
int numToMatch = 4;

Console.WriteLine("{0}", 
   arr.OrderBy(n => Math.Abs(numToMatch - n)).ElementAt(0));

Answer 11

Groovy 28B

f={a,n->a.min{(it-n).abs()}}

Answer 12

Some C# Linq ones... too many ways to do this!

decimal[] nums = { 1, 3, 8, 12 };
decimal target = 4;

var close1 = (from n in nums orderby Math.Abs(n-target) select n).First();
var close2 = nums.OrderBy(n => Math.Abs(n - target)).First();

Console.WriteLine("{0} and {1}", close1, close2);

Even more ways if you use a list instead, since plain ol arrays have no .Sort()

Answer 13

Common Lisp using iterate library.

(defun closest-match (list n)
     (iter (for i in list)
            (finding i minimizing (abs (- i n)))

Answer 14

Language: C, Char count: 79

c(int v,int*a,int A){int n=*a;for(;--A;++a)n=abs(v-*a)<abs(v-n)?*a:n;return n;}

Signature:

int closest(int value, int *array, int array_size);

Usage:

main()
{
    int a[5] = {1, 3, 8, 10, 13};
    printf("%d\n", c(4, a, 5));
}

Answer 15

Perl -- 66 chars:

perl -e 'for(qw/1 3 8 10 13/){$d=($_-4)**2; $c=$_ if not $x or $d<$x;$x=$d;}print $c;'

Answer 16

11 bytes in J:

C=:0{]/:|@-

Examples:

>> a =: 1 3 8 10 13
>> 4 C a
3
>> 11 C a
10
>> 12 C a
13

my breakdown for the layman:

0{         First element of
]          the right argument
/:         sorted by
|          absolute value 
@          of
-          subtraction

Answer 17

Scala (62 chars), based on the idea of the J and Ruby solutions:

def c(l:List[Int],n:Int)=l.sort((a,b)=>(a-n).abs<(b-n).abs)(0)

Usage:

println(c(List(1,3,8,10,13),4))

Answer 18

Shorter Python: 41 chars

f=lambda a,l:min(l,key=lambda x:abs(x-a))

Answer 19

Because I actually needed to do this, here is my PHP

$match = 33;

$set = array(1,2,3,5,8,13,21,34,55,89,144,233,377,610);

foreach ($set as $fib)
    {
     $diff[$fib] = (int) abs($match - $fib);
    }
$fibs = array_flip($diff);
$closest = $fibs[min($diff)];

echo $closest;

Answer 20

41 characters in F#:

let C x = Seq.min_by (fun n -> abs(n-x))

as in

#light

let l = [1;3;8;10;13]

let C x = Seq.min_by (fun n -> abs(n-x))

printfn "%d" (C 4 l)   // 3 
printfn "%d" (C 11 l)  // 10
printfn "%d" (C 12 l)  // 13

Answer 21

Ruby like Python has a min method for Enumerable so you don't need to do a sort.

def c(value, t_array)
  t_array.min{|a,b|  (value-a).abs <=> (value-b).abs }
end

ar = [1, 3, 8, 10, 13]
t = 4
c(t) = 3

Answer 22

Ruby. One pass-through. Handles negative numbers nicely. Perhaps not very short, but certainly pretty.

class Array
  def closest int
    diff = int-self[0]; best = self[0]
    each {|i|
      if (int-i).abs < diff.abs
        best = i; diff = int-i
      end
    }
    best
  end
end

puts [1,3,8,10,13].closest 4

Answer 23

Here's another Haskell answer:

import Control.Arrow
near4 = snd . minimum . map (abs . subtract 4 &&& id)

Answer 24

Haskell, 60 characters -

f a=head.Data.List.sortBy(compare`Data.Function.on`abs.(a-))

Answer 25

Kdb+, 23B:

C:{x first iasc abs x-}

Usage:

q)a:10?20
q)a
12 8 10 1 9 11 5 6 1 5

q)C[a]4
5

Answer 26

Excel VBA - find Excel Range's Index or Value Closest to Target Value

Given an existing Excel Range, rangeOfValues:

1) find index of the closest matching value in the Range using Application.Match (note that the Match method returns a Double)

Dim iMatch as Double 
iMatch = Application.Match(valueToMatch, rangeOfValues)

2) find the closest Range value to the Target Value using VLOOKUP/HLOOKUP

Dim closest as Variant
closest = VLOOKUP(valueToMatch, rangeOfValues)

If an exact match is needed:

Dim exactM as Variant
exactM = VLOOKUP(valueToMatch, rangeOfValues, False)

Answer 27

another PHP answer:

function closestMatch($int, $in) {
    $diffs = array();
    foreach ($in as $i)
        $diffs[abs($int - $i)] = $i;
    ksort($diffs);
    foreach ($diffs as $i) return $i;
}