如何按两个值对地图排序？

Question

I am trying to sort a map by two of its values. First by the timestamp and then by the nonce. In other words, I need to be able to iterate and print the map with the smallest timestamp first, followed by the nonce value. Like this:

    "tx1": Transaction{Value:10, Nonce:1, Timestamp:1563543005},
    "tx2": Transaction{Value:20, Nonce:2, Timestamp:1563543005},
    "tx6": Transaction{Value:60, Nonce:2, Timestamp:1563543005},
    "tx5": Transaction{Value:50, Nonce:4, Timestamp:1563543005},
    "tx7": Transaction{Value:70, Nonce:1, Timestamp:1563543006},
    "tx3": Transaction{Value:30, Nonce:3, Timestamp:1563543006},
    "tx4": Transaction{Value:40, Nonce:4, Timestamp:1563543006},

Here is my code:

https://play.golang.org/p/hXo5clCrlU1

package main

import (
    "fmt"
    "sort"
)

type Transaction struct {
    Value         uint64                        `json:"value"`
    Nonce         uint64                        `json:"nonce"`
    Timestamp     int64                         `json:"timestamp"`
}

func main() {
    // To create a map as input
    memPool := map[string]Transaction {
        "tx1": Transaction{Value:10, Nonce:1, Timestamp:1563543005},
        "tx2": Transaction{Value:20, Nonce:2, Timestamp:1563543005},
        "tx3": Transaction{Value:30, Nonce:3, Timestamp:1563543006},
        "tx4": Transaction{Value:40, Nonce:4, Timestamp:1563543006},
        "tx5": Transaction{Value:50, Nonce:4, Timestamp:1563543005},
        "tx6": Transaction{Value:60, Nonce:2, Timestamp:1563543005},
        "tx7": Transaction{Value:70, Nonce:1, Timestamp:1563543006},
    }


    keys := make([]string, 0, len(memPool))
        for key := range memPool {
            keys = append(keys, key)
        }

        sort.Slice(keys, func(i, j int) bool { return memPool[keys[i]].Timestamp > memPool[keys[j]].Timestamp })


    for _, v := range keys {
        fmt.Println(v)
    }
    fmt.Println("")

    keys2 := make([]string, 0, len(memPool))
        for key2 := range memPool {
            keys2 = append(keys2, key2)
        }

    sort.Slice(keys2, func(i, j int) bool { return memPool[keys2[i]].Nonce > memPool[keys2[j]].Nonce })

    for _, v := range keys2 {
        fmt.Println(v)
    }

}

Current output:

tx7
tx3
tx4
tx1
tx2
tx5
tx6

tx4
tx5
tx3
tx6
tx2
tx7
tx1

Desired output:

tx1
tx2
tx6
tx5
tx7
tx3
tx4

Answer 1

You're sorting two separate times when it appears you want to sort once. So, sort once, using all of the logic that you want to use to sort your values, once.

sort.Slice(keys, func(i, j int) bool {
    if memPool[keys[i]].Timestamp == memPool[keys[j]].Timestamp {
        if memPool[keys[i]].Nonce == memPool[keys[j]].Nonce {
            return memPool[keys[i]].Value < memPool[keys[j]].Value
        }
        return memPool[keys[i]].Nonce < memPool[keys[j]].Nonce
    }
    return memPool[keys[i]].Timestamp < memPool[keys[j]].Timestamp
})

Working example: https://play.golang.org/p/GERCSchEtOf