How to group elements of a slice based on their first occurrence in Go

1 Answer

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package main

import (
    "fmt"
)

func groupElements(arr []int) []int {
    frequency := make(map[int]int)
    order := []int{}
    result := []int{}

    // Count frequencies and track first occurrences
    for _, num := range arr {
        if _, exists := frequency[num]; !exists {
            order = append(order, num)
        }
        frequency[num]++
    }

    // Group elements based on first occurrence
    for _, num := range order {
        for i := 0; i < frequency[num]; i++ {
            result = append(result, num)
        }
    }

    return result
}

func main() {
    vec := []int{88, 33, 77, 88, 22, 55, 88, 55, 11, 99, 88, 11, 77}
    grouped := groupElements(vec)

    fmt.Print("Grouped vector: ")
    for _, num := range grouped {
        fmt.Printf("%d ", num)
    }
    fmt.Println()
}



/*
run:

Grouped vector: 88 88 88 88 33 77 77 22 55 55 11 11 99 

*/

 



answered Oct 10, 2025 by avibootz

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