Search data in array of struct

Technical Discussion
#1

I would like to search data in array of struct.
Var vcustomer :=[]customers
Example : select * from customers stored in vcustomer

Var vorder := []orders
Select * from orders stored in borders

For _,cust range vcustomers{
Find orders,}

How to find customers orders from order array.

One way we can compare.

Is there any other and fast way like indexing and searching

1 Like
#2

If you are searching many times, create a fast data structure, such as a map[customer][]order. If you are doing it just once, then search linearly through the orders slice.

#3

Please give me example

#4

Maybe if you provide some concrete code, I’ll add a few lines to it.

#6

type SudentsMarks struct {

	Student_code int `db:"student_code"`
	Subjectname string `db:"subjectname"`
	Marks   int    `db:"marks"`
}

type Students struct {
Student_code int db:"student_code"
Batch_division string db:"batch_division"
Rollno int db:"rollno"
Name string db:"fullname"
Marks []SudentsMarks
}
var err error
var _students = []Students{}
var _studentsMarks = []SudentsMarks{}

studentquery := select * from students
marksquery := select * from marks

err = Mydb.Select(&studentquery, studentquery)
if err != nil {
return err
}

err = Mydb.Select(&_studentsMarks, marksquery)
if err != nil {
return err
}

now we want to embed marks inside students , because in my student structure marks is array.
we are using linear search

for nstudentloop, student := range _students {

		for _, marksloop := range _studentsMarks {
			if marksloop.student_code == student.student_code {

				_marks := SudentsMarks{}
				_marks.Marks = marksloop.Marks
				_marks.student_code = marksloop.student_code
				_marks.subjectname = marksloop.subjectname

				_students[nstudentloop].Marks = append(_students[nstudentloop].Marks, _marks)
				
			} else {
				break
			}
		}
		

	}

This code is working but according to me there may be better way to solve this issues.
The marks loop run multiple time .

#7

If you create a mapping from student code to Students, then you don’t have to do an O(n^2) nested loop. The following is O(n). I don’t know why you create a new SudentsMarks in the inner loop instead of reusing the one in the slice.

studentsByCode := make(map[int]*Students)
for i := range _students {
  studentsByCode[s[i].Student_code] = &s[i]
}

for _, m := range _studentsMarks {
  s,ok := studentsByCode[m.student_code]
	if ok {
		s.Marks = append(s.Marks, m)
	} else {
		panic("missing student for marks")
	}
}
#9

My requirement is
i want json in this format

{
Student_code : 1
Batch_division : “A”
Rollno : 10
Name : “Mr james”
marks : [ {"Student_code : 1 , Subjectname : “maths”,Marks : 60},
{"Student_code : 1 , Subjectname : “eng”,Marks : 70}]

I am executing 2 separate query . I would like to link both data by using student_code .

#10

You can add “json:…” to the tags in your structs, but you may not even need that. Then you do
json.Marshal(_students).

That what’s the code to build the studentsByCode map does. What is missing?

#11

In your approach . I have to transfer my struct data into map .

using following code according to you.
studentsByCode := make(map[int]*Students)
for i := range _students {
studentsByCode[s[i].Student_code] = &s[i]
}

#12

The map holds a pointer to each struct, so there’s minimal extra memory required and no copying. In terms of space-time tradeoff, there can be a lot of time saved for just a little bit of extra space.

#14

Thank so much it is really fast and perfect logic.

#15

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