json解码键类型

Question

I want to decode a big set of data from a (static-schema) json file. The file contains exclusively numeric data, and keys are all integers. I know how to decode this json into a struct containing fields of map[string]int or map[string]float32 using json.Unmarshal. But I have no interest in string keys, I'd need to convert them to int somehow.

So what I'd like to know is:

1. Is there a way to achieve this, .ie getting a struct containing fields of map[int]float32 type directly from decoding,
2. Otherwise how to achieve this after decoding, in a memory efficient manner ?

Thanks

Answer 1

The JSON format only specifies key/value objects with string keys. Because of this, the encoding/json package only supports string keys as well.

The json/encoding documentation states:

bool, for JSON booleans
float64, for JSON numbers
string, for JSON strings
[]interface{}, for JSON arrays
map[string]interface{}, for JSON objects
nil for JSON null

If you want to use encoding/json package and move it over to a map[int]float64, you can do the following (works with float32 as well):

package main

import (
    "fmt"
    "strconv"
)

func main() {
    a := map[string]float64{"1":1, "2":4, "3":9, "5":25}
    b := make(map[int]float64, len(a))

    for k,v := range a {
        if i, err := strconv.Atoi(k); err == nil {
            b[i] = v
        } else {
            // A non integer key
        }
    }

    fmt.Printf("%#v
", b)
}

Playground