Dynamically add elements from Go struct to JSON

Question content

The output format I want to get is:

{"data": [ [ 0, [ "brendan", "fraser" ] ] , [ 1, [ "keanu", "reeves" ] ] ] }

For this, I defined the following structure:

type actors struct {
    data [][]interface{} `json:"data"`
    }

The individual values ​​brendan, fraser and keanu, reeves come from another one with rec.records[0]. The data structure accessed by value format.

Right now:

rec.records[0].value will correspond to brendan

rec.records[1].value will correspond to fraser and so on.

To assign a value to this structure, I am doing:

numberofactcnt := 0
numberofcolparsed := 0
numberofcolumns := 3

var act actors
var res []actors

    for i := 0; i < 2; i++ {
        numberofactcnt = numberofactcnt + numberofcolparsed
        for j := 0; j < 1; j++ {
            act = actors{[][]interface{}{{i, []string{rec.records[numberofactcnt].value, rec.records[numberofactcnt+1].value}}}}
            re, _ := json.marshal(act)
            fmt.println(string(re))
            numberofcolparsed = numberofcolumns - 1
        }
    }

This gives me the output:

{"data":[[0,["brendan","fraser"]]]}
{"data":[[1,["keanu","reeves"]]]}

How to get the output in this format? ：

{"data": [ [ 0, [ "brendan", "fraser" ] ] , [ 1, [ "keanu", "reeves" ] ] ] }

I think my structure is defined correctly, but how do I append the values ​​to the same json?

Correct answer

First, loop through all the records and store them in data [][]any using append in the slice, then after the loop, , marshalling the results.

numberOfActCnt := 0
numberOfColParsed := 0
numberOfColumns := 3

var res struct { Data [][]any `json:"data"` }
for i := 0; i < 2; i++ {
    numberOfActCnt = numberOfActCnt + numberOfColParsed
    for j := 0; j < 1; j++ {
        res.Data = append(res.Data, []any{i, []string{rec.records[numberOfActCnt].value, rec.records[numberOfActCnt+1].value}})
        numberOfColParsed = numberOfColumns - 1
    }
}
re, err := json.Marshal(res)
if err != nil {
    panic(err)
}
fmt.Println(string(re))

Note: any is an alias of interface{} since go1.18. If you are using an old version of go, you need to continue to use it. interface{}.

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