package main import ( "encoding/json" "errors" ) func splitJSONByClass(jsonData []byte) (map[string][]byte, error) { var data []map[string]interface{} err := json.Unmarshal(jsonData, &data) if err != nil { return nil, err } result := make(map[string][]byte) for _, item := range data { class, ok := item["class"].(string) if !ok { return nil, errors.New("class field is missing or not a string") } jsonItem, err := json.Marshal(item) if err != nil { return nil, err } result[class] = append(result[class], jsonItem) } return result, nil } Ошибка: ./source.go:26:40: cannot use jsonItem (variable of type []byte) as byte value in argument to append

Измените строку result[class] = append(result[class], jsonItem) на result[class] = append(result[class], jsonItem...), чтобы передать срез байтов в качестве аргумента для функции append.

Вот исправленный код:

package main

import (
	"encoding/json"
	"errors"
)

func splitJSONByClass(jsonData []byte) (map[string][]byte, error) {
	var data []map[string]interface{}
	err := json.Unmarshal(jsonData, &data)
	if err != nil {
		return nil, err
	}

	result := make(map[string][]byte)

	for _, item := range data {
		class, ok := item["class"].(string)
		if !ok {
			return nil, errors.New("class field is missing or not a string")
		}

		jsonItem, err := json.Marshal(item)
		if err != nil {
			return nil, err
		}

		result[class] = append(result[class], jsonItem...)
	}

	return result, nil
}