Is there a way to get a list of all the keys in a Go language map? The number of elements is given by len(), but if I have a map like:
m := map[string]string{ "key1":"val1", "key2":"val2" };
How do I iterate over all the keys?
https://play.golang.org/p/JGZ7mN0-U-
for k, v := range m {
fmt.Printf("key[%s] value[%s]\n", k, v)
}
or
for k := range m {
fmt.Printf("key[%s] value[%s]\n", k, m[k])
}
Go language specs for for statements specifies that the first value is the key, the second variable is the value, but doesn't have to be present.
Here's some easy way to get slice of the map-keys.
// Return keys of the given map
func Keys(m map[string]interface{}) (keys []string) {
for k := range m {
keys = append(keys, k)
}
return keys
}
// use `Keys` func
func main() {
m := map[string]interface{}{
"foo": 1,
"bar": true,
"baz": "baz",
}
fmt.Println(Keys(m)) // [foo bar baz]
}
Is there a way to get a list of all the keys in a Go language map?
ks := reflect.ValueOf(m).MapKeys()
how do I iterate over all the keys?
Use the accepted answer:
for _, k := range m { ... }
A Type agnostic solution:
for _, key := range reflect.ValueOf(yourMap).MapKeys() {
value := yourMap.MapIndex(key).Interface()
fmt.Println("Key:", key, "Value:", value)
}
Using Generics:
func Keys[K comparable, V any](m map[K]V) []K {
keys := make([]K, 0, len(m))
for k := range m {
keys = append(keys, k)
}
return keys
}
For sorted keys of map[string]string.
package main
import (
"fmt"
"sort"
)
func main() {
m := map[string]string{"key1": "val1", "key2": "val2"}
sortStringMap(m)
}
// sortStringMap prints the [string]string as keys sorted
func sortStringMap(m map[string]string) {
var keys []string
for key := range m {
keys = append(keys, key)
}
sort.Strings(keys) // sort the keys
for _, key := range keys {
fmt.Printf("%s\t:%s\n", key, m[key])
}
}
output:
key1 :val1
key2 :val2
Related
I want to remove range of slice from slice like remove "A", "B" from "A" to "Z", but I want to make it efficient (I don't know why in Go but in Python we can use hashmap).
The code below is the closest I can get but there are edge cases I miss:
func removeString(listOri []string, targetDelete []string) []string {
newitems := []string{}
for i := range listOri {
for j := range targetDelete {
if listOri [i] != targetDelete[j] {
newitems = append(newitems, listOri [i])
}
}
}
return newitems
}
listOriginal := []string{"A", "B", "C", "D"}
listDelete := []string{"A", "B"}
listNew := removeString(listOriginal, listDelete)
result = "A","B","C","C","D","D"
It's better (faster) to use a map to represent the items that are to be deleted. If there's N things in the original list, and M things that are in the to-be-deleted list, your code (once the bugs are fixed) would run in O(NM) time, whereas a map-based solution will run in O(N) time.
Here's example code:
package main
import "fmt"
func filter(src []string, del map[string]bool) []string {
var dst []string
for _, s := range src {
if !del[s] {
dst = append(dst, s)
}
}
return dst
}
func main() {
src := []string{"A", "B", "C", "D"}
del := map[string]bool{"A": true, "B": true}
fmt.Println(filter(src, del))
}
If you really need the to-be-deleted things to be a slice, you should convert the slice into a map first. Then the code is O(N+M) time.
What you need to do is check if each item in the original exists in the list of items to delete, and if not then you add it to the result:
func removeString(listOri []string, targetDelete []string) []string {
newitems := []string{}
var found bool
for i := range listOri {
found = false
for j := range targetDelete {
if listOri[i] == targetDelete[j] {
found = true
break
}
}
if !found {
newitems = append(newitems, listOri[i])
}
}
return newitems
}
You might also find Does Go have "if x in" construct similar to Python? informative.
Let's say I have a list of student cities and the size of it could be 100 or 1000, and I want to filter out all duplicates cities.
I want a generic solution that I can use to remove all duplicate strings from any slice.
I am new to Go Language, So I tried to do it by looping and checking if the element exists using another loop function.
Students' Cities List (Data):
studentsCities := []string{"Mumbai", "Delhi", "Ahmedabad", "Mumbai", "Bangalore", "Delhi", "Kolkata", "Pune"}
Functions that I created, and it's doing the job:
func contains(s []string, e string) bool {
for _, a := range s {
if a == e {
return true
}
}
return false
}
func removeDuplicates(strList []string) []string {
list := []string{}
for _, item := range strList {
fmt.Println(item)
if contains(list, item) == false {
list = append(list, item)
}
}
return list
}
My solution test
func main() {
studentsCities := []string{"Mumbai", "Delhi", "Ahmedabad", "Mumbai", "Bangalore", "Delhi", "Kolkata", "Pune"}
uniqueStudentsCities := removeDuplicates(studentsCities)
fmt.Println(uniqueStudentsCities) // Expected output [Mumbai Delhi Ahmedabad Bangalore Kolkata Pune]
}
I believe that the above solution that I tried is not an optimum solution. Therefore, I need help from you guys to suggest the fastest way to remove duplicates from the slice?
I checked StackOverflow, this question is not being asked yet, so I didn't get any solution.
I found Burak's and Fazlan's solution helpful. Based on that, I implemented the simple functions that help to remove or filter duplicate data from slices of strings, integers, or any other types with generic approach.
Here are my three functions, first is generic, second one for strings and last one for integers of slices. You have to pass your data and return all the unique values as a result.
Generic solution: => Go v1.18
func removeDuplicate[T string | int](sliceList []T) []T {
allKeys := make(map[T]bool)
list := []T{}
for _, item := range sliceList {
if _, value := allKeys[item]; !value {
allKeys[item] = true
list = append(list, item)
}
}
return list
}
To remove duplicate strings from slice:
func removeDuplicateStr(strSlice []string) []string {
allKeys := make(map[string]bool)
list := []string{}
for _, item := range strSlice {
if _, value := allKeys[item]; !value {
allKeys[item] = true
list = append(list, item)
}
}
return list
}
To remove duplicate integers from slice:
func removeDuplicateInt(intSlice []int) []int {
allKeys := make(map[int]bool)
list := []int{}
for _, item := range intSlice {
if _, value := allKeys[item]; !value {
allKeys[item] = true
list = append(list, item)
}
}
return list
}
You can update the slice type, and it will filter out all duplicates data for all types of slices.
Here is the GoPlayground link: https://go.dev/play/p/iyb97KcftMa
Adding this answer which worked for me, does require/include sorting, however.
func removeDuplicateStrings(s []string) []string {
if len(s) < 1 {
return s
}
sort.Strings(s)
prev := 1
for curr := 1; curr < len(s); curr++ {
if s[curr-1] != s[curr] {
s[prev] = s[curr]
prev++
}
}
return s[:prev]
}
For fun, I tried using generics! (Go 1.18+ only)
type SliceType interface {
~string | ~int | ~float64 // add more *comparable* types as needed
}
func removeDuplicates[T SliceType](s []T) []T {
if len(s) < 1 {
return s
}
// sort
sort.SliceStable(s, func(i, j int) bool {
return s[i] < s[j]
})
prev := 1
for curr := 1; curr < len(s); curr++ {
if s[curr-1] != s[curr] {
s[prev] = s[curr]
prev++
}
}
return s[:prev]
}
Go Playground Link with tests: https://go.dev/play/p/bw1PP1osJJQ
You can do in-place replacement guided with a map:
processed := map[string]struct{}{}
w := 0
for _, s := range cities {
if _, exists := processed[s]; !exists {
// If this city has not been seen yet, add it to the list
processed[s] = struct{}{}
cities[w] = s
w++
}
}
cities = cities[:w]
reduce memory usage:
package main
import (
"fmt"
"reflect"
)
type void struct{}
func main() {
digits := [6]string{"one", "two", "three", "four", "five", "five"}
set := make(map[string]void)
for _, element := range digits {
set[element] = void{}
}
fmt.Println(reflect.ValueOf(set).MapKeys())
}
p.s. playground
Simple to understand.
func RemoveDuplicate(array []string) []string {
m := make(map[string]string)
for _, x := range array {
m[x] = x
}
var ClearedArr []string
for x, _ := range m {
ClearedArr = append(ClearedArr, x)
}
return ClearedArr
}
If you want to don't waste memory allocating another array for copy the values, you can remove in place the value, as following:
package main
import "fmt"
var studentsCities = []string{"Mumbai", "Delhi", "Ahmedabad", "Mumbai", "Bangalore", "Delhi", "Kolkata", "Pune"}
func contains(s []string, e string) bool {
for _, a := range s {
if a == e {
return true
}
}
return false
}
func main() {
fmt.Printf("Cities before remove: %+v\n", studentsCities)
for i := 0; i < len(studentsCities); i++ {
if contains(studentsCities[i+1:], studentsCities[i]) {
studentsCities = remove(studentsCities, i)
i--
}
}
fmt.Printf("Cities after remove: %+v\n", studentsCities)
}
func remove(slice []string, s int) []string {
return append(slice[:s], slice[s+1:]...)
}
Result:
Cities before remove: [Mumbai Delhi Ahmedabad Mumbai Bangalore Delhi Kolkata Pune]
Cities after remove: [Ahmedabad Mumbai Bangalore Delhi Kolkata Pune]
It can also be done with a set-like map:
ddpStrings := []string{}
m := map[string]struct{}{}
for _, s := range strings {
if _, ok := m[scopeStr]; ok {
continue
}
ddpStrings = append(ddpStrings, s)
m[s] = struct{}{}
}
func UniqueNonEmptyElementsOf(s []string) []string {
unique := make(map[string]bool, len(s))
var us []string
for _, elem := range s {
if len(elem) != 0 {
if !unique[elem] {
us = append(us, elem)
unique[elem] = true
}
}
}
return us
}
send the duplicated splice to the above function, this will return the splice with unique elements.
func main() {
studentsCities := []string{"Mumbai", "Delhi", "Ahmedabad", "Mumbai", "Bangalore", "Delhi", "Kolkata", "Pune"}
uniqueStudentsCities := UniqueNonEmptyElementsOf(studentsCities)
fmt.Println(uniqueStudentsCities)
}
Here's a mapless index based slice's duplicate "remover"/trimmer. It use a sort method.
The n value is always 1 value lower than the total of non duplicate elements that's because this methods compare the current (consecutive/single) elements with the next (consecutive/single) elements and there is no matches after the lasts so you have to pad it to include the last.
Note that this snippet doesn't empty the duplicate elements into a nil value. However since the n+1 integer start at the duplicated item's indexes, you can loop from said integer and nil the rest of the elements.
sort.Strings(strs)
for n, i := 0, 0; ; {
if strs[n] != strs[i] {
if i-n > 1 {
strs[n+1] = strs[i]
}
n++
}
i++
if i == len(strs) {
if n != i {
strs = strs[:n+1]
}
break
}
}
fmt.Println(strs)
Based on Riyaz's solution, you can use generics since Go 1.18
func removeDuplicate[T string | int](tSlice []T) []T {
allKeys := make(map[T]bool)
list := []T{}
for _, item := range tSlice {
if _, value := allKeys[item]; !value {
allKeys[item] = true
list = append(list, item)
}
}
return list
}
Generics minimizes code duplication.
Go Playground link : https://go.dev/play/p/Y3fEtHJpP7Q
So far #snassr has given the best answer as it is the most optimized way in terms of memory (no extra memory) and runtime (nlogn). But one thing I want to emphasis here is if we want to delete any index/element of an array we should loop from end to start as it reduces complexity. If we loop from start to end then if we delete nth index then we will accidentally miss the nth element (which was n+1th before deleting nth element) as in the next iteration we will get the n+1th element.
Example Code
func Dedup(strs []string) {
sort.Strings(strs)
for i := len(strs) - 1; i > 0; i-- {
if strs[i] == strs[i-1] {
strs = append(strs[:i], strs[i+1:]...)
}
}
}
try: https://github.com/samber/lo#uniq
names := lo.Uniq[string]([]string{"Samuel", "John", "Samuel"})
// []string{"Samuel", "John"}
I'm trying to unmarshal a JSON array of the following type:
[
{"abc's": "n;05881364"},
{"abcoulomb": "n;13658345"},
{"abcs": "n;05881364"}
]
into a map[string]string. This question Golang parse JSON array into data structure almost answered my problem, but mine is a truly map, not an array of maps. Unmarshaling into a []map[string]string worked but I now get a map of map[string]string, not a simple map of string as it should be
There is no way to do it directly with the json package; you have to do the conversion yourself. This is simple:
package main
import (
"encoding/json"
"fmt"
)
func main() {
data := []byte(`
[
{"abc's": "n;05881364"},
{"abcoulomb": "n;13658345"},
{"abcs": "n;05881364"}
]
`)
var mapSlice []map[string]string
if err := json.Unmarshal(data, &mapSlice); err != nil {
panic(err)
}
resultingMap := map[string]string{}
for _, m := range mapSlice {
for k, v := range m {
resultingMap[k] = v
}
}
fmt.Println(resultingMap)
}
Output
map[abc's:n;05881364 abcoulomb:n;13658345 abcs:n;05881364]
An alternative (though very similar) to Alex's answer is to define your own type along with an UnmarshalJSON function.
package main
import (
"encoding/json"
"fmt"
)
type myMapping map[string]string
func (mm myMapping) UnmarshalJSON(b []byte) error {
var temp []map[string]string
if err := json.Unmarshal(b, &temp); err != nil {
return err
}
for _, m := range temp {
for k, v := range m {
mm[k] = v
}
}
return nil
}
func main() {
data := []byte(`
[
{"abc's": "n;05881364"},
{"abcoulomb": "n;13658345"},
{"abcs": "n;05881364"}
]`)
resultingMap := myMapping{}
if err := json.Unmarshal(data, &resultingMap); err != nil {
panic(err)
}
fmt.Println(resultingMap)
}
Playground
New to Golang, Yesterday I've started to play with Golang and wrote some code which was actually written in PHP. I just wanted to see difference in performance.
I am doing the exact same thing in PHP response is exact same in http request but the Golang is performing really slow even after compiling it.
I am trying to understand what things that I am using in Golang I shouldn't be using and how can I improve performance in this piece of Code.
I know Iterating over map is slow but PHP using hash maps for implementing multidimentional arrays, well. I can gurantee the sql queries I used were exact same copy pasted from PHP, machines are same, and loop numbers are same in both codes.
package main
import (
"database/sql"
"encoding/json"
"fmt"
_ "github.com/go-sql-driver/mysql"
"net/http"
"reflect"
"strings"
)
func main() {
db, err := sql.Open("mysql", "***:****#tcp(****:3306)/****")
fmt.Println(reflect.TypeOf(db))
checkErr(err)
fmt.Println("Handle Request setup... OK")
http.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
jsonData, err := getListings(db)
checkErr(err)
w.Write([]byte(jsonData))
})
fmt.Println("Starting Server....")
fmt.Println("Listening on port 8081")
http.ListenAndServe(":8081", nil)
}
func getListings(db *sql.DB) ([]byte, error) {
var userId string = "142"
normalListings := sqlToArray(db, `******`)
manualListings := sqlToArray(db, "******")
var groupIds []string
for key := range manualListings {
groupId := "142," + manualListings[key]["group_id"]
if !stringInSlice(groupId, groupIds) {
groupIds = append(groupIds, groupId)
}
}
var groupIdsString string
groupIdsString = strings.Join(groupIds, ", ")
manualGroups := sqlToArray(db, "*****")
for key := range manualListings {
for key2 := range manualGroups {
groupId := "142," + manualListings[key]["group_id"]
if groupId == manualGroups[key]["ticket_id"] {
entry := make(map[string]string)
entry["ticket_id"] = manualListings[key]["listing_id"]
entry["date_created"] = manualGroups[key2]["date_created"]
normalListings = append(normalListings, entry)
}
}
}
return json.Marshal(normalListings)
}
func stringInSlice(a string, list []string) bool {
for _, b := range list {
if b == a {
return true
}
}
return false
}
func sqlToArray(db *sql.DB, sqlString string) []map[string]string {
rows, err := db.Query(sqlString)
checkErr(err)
columns, err := rows.Columns()
count := len(columns)
values := make([]interface{}, count)
valuePtrs := make([]interface{}, count)
tableData := make([]map[string]string, 0)
for rows.Next() {
for i := 0; i < count; i++ {
valuePtrs[i] = &values[i]
}
rows.Scan(valuePtrs...)
entry := make(map[string]string)
for i, col := range columns {
val := values[i]
b, ok := val.([]byte)
if ok {
entry[col] = string(b)
} else {
entry[col] = string(b)
}
}
tableData = append(tableData, entry)
}
return tableData
}
func checkErr(err error) {
if err != nil {
panic(err)
}
}
Edits:
Changed the code to use statically typed structs instead of using maps and Identified the problematic piece of code
New code:
package main
import (
"database/sql"
"encoding/json"
"fmt"
_ "github.com/go-sql-driver/mysql"
"net/http"
"strings"
)
type listingsType struct {
TicketId string
DateCreated string
}
func main() {
db, err := sql.Open("mysql", "******")
checkErr(err)
fmt.Println("Handle Request setup... OK")
http.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
jsonData, err := getListings(db)
checkErr(err)
w.Write([]byte(jsonData))
})
fmt.Println("Starting Server....")
fmt.Println("Listening on port 8081")
http.ListenAndServe(":8081", nil)
}
func getListings(db *sql.DB) ([]byte, error) {
var userId string = "142"
normalListings := sqlToArray(db, `*****`)
manualListings := sqlToArray(db, "*****")
var groupIds []string
for _, elem := range manualListings {
groupId := "142," + elem.DateCreated
if !stringInSlice(groupId, groupIds) {
groupIds = append(groupIds, groupId)
}
}
var groupIdsString string
groupIdsString = strings.Join(groupIds, ", ")
fmt.Println(groupIdsString)
manualGroups := sqlToArray(db, "******")
for _, manualList := range manualListings {
for _, manualGroup := range manualGroups {
groupId := "142," + manualList.DateCreated
if groupId == manualGroup.TicketId {
var entry listingsType
entry.TicketId = manualList.TicketId
entry.DateCreated = manualGroup.DateCreated
normalListings = append(normalListings, entry)
}
}
}
return json.Marshal(normalListings)
}
func stringInSlice(a string, list []string) bool {
for _, b := range list {
if b == a {
return true
}
}
return false
}
func sqlToArray(db *sql.DB, sqlString string) []listingsType {
rows, err := db.Query(sqlString)
checkErr(err)
tableData := []listingsType{}
for rows.Next() {
var entry listingsType
rows.Scan(&entry.TicketId, &entry.DateCreated)
tableData = append(tableData, entry)
}
return tableData
}
func checkErr(err error) {
if err != nil {
panic(err)
}
}
Problematic piece of code
As soon as I comment the following block of code the my code performs just fine.
Any idea what is wrong with this loop ?
for _, manualList := range manualListings {
for _, manualGroup := range manualGroups {
groupId := "142," + manualList.DateCreated
if groupId == manualGroup.TicketId {
var entry listingsType
entry.TicketId = manualList.TicketId
entry.DateCreated = manualGroup.DateCreated
normalListings = append(normalListings, entry)
}
}
}
Profiling Result
Ok So got it fixed by the way. I brought the request time from 5k+ MS to 500 MS, now finally my PHP code is slower which is 900 MS
I got rid of the inner loop to search by implementing a separate function to get SQL data in a different data structure in key value of maps instead of searching whole arrays I created the value as key which I was looking for in array, This way I got rid of the second loop which was making trouble by linear search on strings.
manualGroups := sqlToArraySpecial(db, "****")
for _, manualList := range manualListings {
//index := stringInSliceArray(manualList.DateCreated, manualGroups)
groupId := "142," + manualList.DateCreated
var entry listingsType
entry.TicketId = manualList.TicketId
entry.DateCreated = manualGroups[groupId]
normalListings = append(normalListings, entry)
}
and here is my new SQL function
func sqlToArraySpecial(db *sql.DB, sqlString string) map[string]string {
rows, err := db.Query(sqlString)
checkErr(err)
tableData := make(map[string]string)
for rows.Next() {
var date_created string
var ticket_id string
rows.Scan(&ticket_id, &date_created)
//fmt.Println(ticket_id)
tableData[ticket_id] = date_created
}
return tableData
}
although this is a dead post, I cannot help but note since no one else has (explicitly), and it's kinda' important to know why:
nested for loops exhibit quadratic running time complexity,
and as you stated, searching an array takes linear time,
so simply put:
the computation time will increase by the square of the total number of elements.
now to answer why this isn't the case in php -- well cause you were using a hash map which:
can be said, exhibits a constant time complexity
again, simply put this means that:
look up time is not related to the number of elements (aka the size of the collection).
see: big-o
with all that being said, please note:
i don't know php,
thus do not the know details regarding how the language implements arrays, and
im not an algorithm expert,
so please treat my post as a statement for the general case.
pce
Is there a way to convert struct to array of values in Golang?
for example if I have this kind of struct (not just this one):
type Model struct {
Id bson.ObjectId `bson:"_id,omitempty"`
CreatedAt time.Time `bson:",omitempty"`
UpdatedAt time.Time `bson:",omitempty"`
DeletedAt time.Time `bson:",omitempty"`
CreatedBy bson.ObjectId `bson:",omitempty"`
UpdatedBy bson.ObjectId `bson:",omitempty"`
DeletedBy bson.ObjectId `bson:",omitempty"`
Logs []bson.ObjectId `bson:",omitempty"`
}
type User struct {
Name string `bson:"name"`
Model `bson:",inline"`
}
The case was, I usually send the JSON to the browser with this format:
var iota = -1
var data = {
NAME: ++iota, ID: ++iota, CREATED_AT: ++iota, UPDATED_AT: ++iota, DELETED_AT: ++iota, // and so on
rows: [['kiz',1,'2014-01-01','2014-01-01','2014-01-01'],
['yui',2,'2014-01-01','2014-01-01','2014-01-01'],
['ham',3,'2014-01-01','2014-01-01','2014-01-01'] // and so on
]
};
Instead of:
var data = {
rows: [{NAME:'kiz',ID:1,CreatedAt:'2014-01-01',UpdatedAt:'2014-01-01',DeletedAt:'2014-01-01'},
{NAME:'yui',ID:2,CreatedAt:'2014-01-01',UpdatedAt:'2014-01-01',DeletedAt:'2014-01-01'},
{NAME:'ham',ID:3,CreatedAt:'2014-01-01',UpdatedAt:'2014-01-01',DeletedAt:'2014-01-01'} // and so on
]
}
Here's what I've tried:
import (
"github.com/kr/pretty"
//"gopkg.in/mgo.v2"
"gopkg.in/mgo.v2/bson"
"reflect"
"runtime"
"strings"
"time"
)
// copy the model from above
func Explain(variable interface{}) {
_, file, line, _ := runtime.Caller(1)
//res, _ := json.MarshalIndent(variable, " ", " ")
res := pretty.Formatter(variable)
fmt.Printf("%s:%d: %# v\n", file[len(FILE_PATH):], line, res)
//spew.Dump(variable)
}
func s2a(i interface{}) []interface{} { // taken from https://gist.github.com/tonyhb/5819315
iVal := reflect.ValueOf(i).Elem()
//typ := iVal.Type()
values := make([]interface{}, 0, iVal.NumField())
for i := 0; i < iVal.NumField(); i++ {
f := iVal.Field(i)
//tag := typ.Field(i).Tag.Get("tagname")
//fmt.Println(tag)
// name := typ.Field(i).Name
v := f.Interface()
switch v.(type) {
case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, string, []byte, time.Time:
// do nothing
// case struct{}: // how to catch any embeeded struct?
case Model: // Model (or any embedded/nameless struct) should also converted to array
//arr := s2a() // invalid type assertion: f.(Model) (non-interface type reflect.Value on left)
//arr := s2a(f.Addr().(&Model)) // invalid type assertion: f.Addr().(&Model) (non-interface type reflect.Value on left)
// umm.. how to convert f back to Model?
//for _, e := range arr {
values = append(values, e)
//}
default: // struct? but also interface and map T_T
//v = s2a(&v)
}
values = append(values, v)
}
return values
}
func main() {
//sess, err := mgo.Dial("127.0.0.1")
//Check(err, "unable to connect")
//db := sess.DB("test")
//coll := db.C("coll1")
user := User{}
user.Id = bson.NewObjectId()
user.Name = "kis"
//changeInfo, err := coll.UpsertId(user.Id, user)
//Check(err, "failed to insert")
//Explain(changeInfo)
//Explain(s2a(changeInfo))
user.Name = "test"
Explain(user)
Explain(s2a(&user))
//err = coll.FindId(user.Id).One(&user)
//Check(err, "failed to fetch")
//Explain(user)
//Explain(s2a(&user))
user.CreatedAt = time.Now()
//err = coll.UpdateId(user.Id, user)
//Check(err, "failed to update")
Explain(changeInfo)
Explain(s2a(&user))
user.CreatedAt = user.DeletedAt
//err = coll.FindId(user.Id).One(&user)
//Check(err, "failed to fetch")
Explain(user)
Explain(s2a(&user))
}
Is there easy/fast way to convert struct to array (and if there struct embedded/inside it, converted to array also)?
If you are happy to specify a fixed order for the fields in the array representation, you could do this by implementing the json.Marshaler interface to customise its representation. For example:
func (u User) MarshalJSON() ([]byte, error) {
a := []interface{}{
u.Name,
u.Id,
...,
}
return json.Marshal(a)
}
Now when you marshal variables of this type, they will be represented as an array. If you want to also do the reverse (unmarshal an array into this struct), you will also need to implement the json.Unmarshaler interface. This could be done in a similar fashion, using json.Unmarshal to decode into a []interface{} slice and then pull out the values. Make sure UnmarshalJSON is declared to take a pointer receiver though, or your code won't work (you'll end up updating a copy of the struct rather than the struct itself).
Why not use reflect.Kind()? Here's the playground: http://play.golang.org/p/YjbsnB4eln
Use the reflect package.
Here's some playground code that'll work for one record (of any struct type), you can refactor it to work for a slice of records.
EDIT: (copy-pasted for good measure)
package main
import "fmt"
import "strings"
import "reflect"
type X struct {
Y string
Z int
}
func main() {
data := X{"yval",3}
expectedResult := `{"Y": 0, "Z": 1, "rows": [["yval", 3]]}`
fmt.Println(convert(data))
fmt.Println(expectedResult)
}
func convert(data interface{}) string {
v := reflect.ValueOf(data)
n := v.NumField()
st := reflect.TypeOf(data)
headers := make([]string, n)
for i := 0; i < n; i++ {
headers[i] = fmt.Sprintf(`"%s": %d`, st.Field(i).Name, i)
}
rowContents := make([]string, n)
for i := 0; i < n; i++ {
x := v.Field(i)
s := fmt.Sprintf("%v", x.Interface())
if x.Type().String() == "string" {
s = `"` + s + `"`
}
rowContents[i] = s
}
return "{" + strings.Join(headers, ", ") + `, "rows": [[` + strings.Join(rowContents, ", ") + "]]}"
}