How to sort by time.Time

Question

I am trying to sort struct in Go by its member which is of type time.Time. the structure is as follows.

type reviews_data struct {
    review_id string
    date time.Time
    score int
    firstname string
    anonymous bool
    review_text string
    title_text string
    rating float64
    upcount int
}

I have the below functions for sorting

type timeSlice []reviews_data

// Forward request for length
func (p timeSlice) Len() int {
    return len(p) 
}

// Define compare
func (p timeSlice) Less(i, j int) bool {
    return p[i].date.Before(p[j].date)
}

// Define swap over an array
func (p timeSlice) Swap(i, j int) {
    p[i], p[j] = p[j], p[i] 
}

A map is defined as follows

var reviews_data_map = make(map[string]reviews_data)

After the map gets filled with values,sorting of the map by values is done as below

//Sort the map by date
    date_sorted_reviews := make(timeSlice, 0, len(reviews_data_map))
    for _, d := range reviews_data_map {
        date_sorted_reviews = append(date_sorted_reviews, d)
    }       
    sort.Sort(date_sorted_reviews)

The problem is that the result is not sorted.Can anyone tell me what the problem is.

Answer 1

Go 1.8 and above:

sort.Slice(timeSlice, func(i, j int) bool {
    return timeSlice[i].date.Before(timeSlice[j].date)
})

Answer 2

It looks sorted to me:

package main

import (
    "fmt"
    "sort"
    "time"
)

type reviews_data struct {
    review_id   string
    date        time.Time
    score       int
    firstname   string
    anonymous   bool
    review_text string
    title_text  string
    rating      float64
    upcount     int
}

type timeSlice []reviews_data

func (p timeSlice) Len() int {
    return len(p)
}

func (p timeSlice) Less(i, j int) bool {
    return p[i].date.Before(p[j].date)
}

func (p timeSlice) Swap(i, j int) {
    p[i], p[j] = p[j], p[i]
}

func main() {
    var reviews_data_map = make(map[string]reviews_data)
    reviews_data_map["1"] = reviews_data{date: time.Now().Add(12 * time.Hour)}
    reviews_data_map["2"] = reviews_data{date: time.Now()}
    reviews_data_map["3"] = reviews_data{date: time.Now().Add(24 * time.Hour)}
    //Sort the map by date
    date_sorted_reviews := make(timeSlice, 0, len(reviews_data_map))
    for _, d := range reviews_data_map {
        date_sorted_reviews = append(date_sorted_reviews, d)
    }
    fmt.Println(date_sorted_reviews)
    sort.Sort(date_sorted_reviews)
    fmt.Println(date_sorted_reviews)
}

Output:

[{ {63393534000 0 0x1ba3e0} 0  false   0 0} { {63393490800 0 0x1ba3e0} 0  false   0 0} { {63393577200 0 0x1ba3e0} 0  false   0 0}]
[{ {63393490800 0 0x1ba3e0} 0  false   0 0} { {63393534000 0 0x1ba3e0} 0  false   0 0} { {63393577200 0 0x1ba3e0} 0  false   0 0}]

Answer 3

This can be done below go 1.8 without the extra type and map in the accepted answer.

package main

import (
    "fmt"
    "time"
    "sort"
)

type reviews_data struct {
    review_id   string
    date        time.Time
}

func main() {
    fmt.Println("Sort Example")
    var listOfReviews = make([]reviews_data, 0)
    listOfReviews = append(listOfReviews, reviews_data{review_id: "1",date:time.Now()})
    listOfReviews = append(listOfReviews, reviews_data{review_id: "2",date: time.Now().AddDate(0, 0, 7*1)})
    listOfReviews = append(listOfReviews, reviews_data{review_id: "1",date: time.Now().AddDate(0, 0, 7*-1)})

    sort.Slice(listOfReviews, func(i, j int) bool { return listOfReviews[i].date.Before(listOfReviews[j].date) })
}