sorting int slice in golang

Question

say I have an int slice containing the following numbers: 2781,4706,1347,1192,3087,2920,198,2312,930,3284,1677,3687,2011,4107,4148,4195,2159,1263,2918,2503

I want to sort them based on how close they are away from a certain value. For example, say my value was 1200.

My slice after being sorted would be: 1192,1263,1347,1677,2011,2159,2312,2503,2781,2918,2920,3087,3284,3687,4107,4148,4195,4706,930,198

I tried the approach of iterating through the array, subtracting my specified value, then sorting in ascending order ultimately adding the value again to return to my original number. This approach wouldn't work in all test cases, and I know its bad practice since I'm mutating the array.

I think your best bet would be to write a custom type that satisfies the `sort.Interface` type. More info is in the [package documentation](https://golang.org/pkg/sort/). — squiguy, Jul 31 '18 at 21:06
Note, 930 is not that far from 1200 that it should be at the end of the sorted array. I'll post a full solution below. — Tinkerer, Jun 13 '21 at 17:36

maerics · Accepted Answer · 2018-07-31T22:09:30.233

One approach would be to use sort.Slice(...) with a "less" (comparator) function that simply returns the lesser of the distance of the two given values from the target value.

For example (Go Playground):

func main() {
  xs := []int{2781, 4706, 1347, 1192, 3087, 2920, 198, 2312, 930, 3284, 1677, 3687, 2011, 4107, 4148, 4195, 2159, 1263, 2918, 2503}
  sortByDistanceFrom(1200, xs)
  fmt.Println(xs)
  // [1192 1263 1347 930 1677 2011 2159 198 2312 2503 2781 2918 2920 3087 3284 3687 4107 4148 4195 4706]

}

func sortByDistanceFrom(x int, xs []int) {
  sort.Slice(xs, func(i, j int) bool {
    di := math.Abs(float64(x - xs[i]))
    dj := math.Abs(float64(x - xs[j]))
    return di < dj
  })
}

Note that the fourth value returned by this example is 930 instead of 1677 produced by your sample output because it computes the absolute distance to the target number (|1200-1677|=433 > |1200-930|=270). If you want to prefer values greater than the target to values less than the target then you would have to modify your comparator function accordingly.

sorting int slice in golang

1 Answers1