How could I pick a random item from a slice with bias towards one end of the slice using Go?

I understand one way to pick a random value from a slice in Go:

rand.Seed(time.Now().UTC().UnixNano())     
                                                
var db [500]string                         
log.Println(db[rand.Intn(len(db))])        

But how would I pick a random item from the slice, with a bias towards one end of the slice? For my use case I'll have a slice that grows over time using append(). My understanding is that the newest items will be added to the right-hand side of the slice. I'd like to create a function that picks a random item from the slice, with bias towards the newest members of the slice. My first guess is to use a normal distribution via rand.NormFloat64(), but I'm not sure how or if I can use it to achieve this.

The function should be capable of picking any item from the slice, but should pick new items added to the slice at a much higher frequency.

Assuming you're happy with the normal distribution, you can use rand.Normfloat64(). If your array has 20 items:

int(math.Abs(rand.NormFloat64())*10) % 20

Will produce numbers that are weighted toward the start of the list. And

20 - int(math.Abs(rand.NormFloat64())*10) % 20

Will produce numbers that are weighted toward the end of the list.

Here's an example that demonstrates a sample random distribution.
On go playground: https://go.dev/play/p/AwEPEzQO7P8

package main

import (
	"fmt"
	"math"
	"math/rand"
)
func main() {
	var buckets [20]int
	for i := 0; i < 1000; i++ {
		r := int(math.Abs(rand.NormFloat64())*10) % 20
		buckets[r]++
	}
	fmt.Println(buckets)
}

Sample output:

[86 92 76 80 73 69 60 69 58 51 47 38 44 30 29 24 19 27 18 10]

It's random though, so you could still get all tail end items ....

If you want a step function where the numbers of the first half are 10x the numbers of the left, just use two rands.

n := rand.Intn(10)
if rand.Float64() < 0.1 {
    n = n + 10
}

Example on go playground: https://go.dev/play/p/CitUsHmwQez

package main

import (
	"fmt"
	"math/rand"
)

func main() {
	var buckets [20]int
	for i := 0; i < 1000; i++ {
		r := rand.Intn(10)
		if rand.Float64() < 0.1 {
			r = r + 10
		}
		buckets[r]++
	}
	fmt.Println(buckets)
}

Sample output

[96 92 89 89 88 78 95 86 83 98 15 10 15 10 10 12 4 11 11 8]