Group and Sum slices

[Marcos Bortolussi]

Hi, I come from the .NET world where I had LINQ so i could do in memory queries like the one we usually see in SQL.

I have a slice of this structure I want to group by 8 fields, and then sum another integer field. Something like:

type Register struct {

id1 int

id2 int

id3 int

id4 int

id5 int

id6 int

id7 int

id8 int

money int

}

I thought in:

1.  Creating an Equal function, to compare structures (those eight fields).
   
2. Iterate over the collection I'm analyzing. 
1. For each item check if it is already in the hash table.
2. If it is there => I sum the field.
3. If it is not => I add the new item to hash table.

Is there a better way or any beautiful, perforfomant and easy ready to use library?

[Caleb Doxsey]

Go doesn't have LINQ, but it does have a database/sql package. If you're not afraid of using strings, probably the cleanest way to do this would be to use sqlite, an embedded database, that understands SQL and has support for in-memory tables. Here's a go binding:

https://godoc.org/github.com/mattn/go-sqlite3

And an example:

https://astaxie.gitbooks.io/build-web-application-with-golang/content/en/05.3.html

You can use the special string: :memory: for an in-memory table rather than one stored on disk.

If you're looking for something less generic, but still fairly clean, you can use a struct as a key in a hash table: https://play.golang.org/p/1CIpvWd0jZ

type Key struct {

id1, id2, id3 int // etc

}

type Record struct {

Key

money int

}

func main() {

records := []Record{

{Key{1, 2, 3}, 1000},

{Key{1, 2, 3}, 500},

{Key{1, 2, 3}, 100},

}

m := map[Key]int{}

for _, r := range records {

m[r.Key] += r.money

}

fmt.Println(m)

// map[{1 2 3}:1600]

}