How to write List to Json in scientific notation in c#?

Question

I'm trying to serialize List to json file like this

class ScientificDoubleConverter : JsonConverter
{
  public override bool CanRead { get { return true; } }
  public override bool CanConvert(Type objectType)
  {
    return true;
  }

  public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
  {
    if (value is List<double> myList)
    {

      JArray myArray = new JArray();
      myList.ForEach(dblValue => myArray.Add(dblValue.ToString("E")));
      myArray.WriteTo(writer);

    }
  }
}

This works, but i get values with qoutes

"values": ["-9,811880E-002", "2,236657E-002", "-4,020144E-001", ...

I would like no quotes and a point in value scientific notation

"values": [-9.811880E-002, 2.236657E-002, -4.020144E-001, ...

Why do you care what format the JSON uses? It will be converted back to doubles when you deserialise it. — Matthew Watson, Nov 14 '19 at 15:21
If MathLab reads JSON, then it won't care either? I really don't understand why it must be formatted this way... — Matthew Watson, Nov 14 '19 at 15:24
is there chance you could convert to scientific notation in javascript or you need it as in json? — sairfan, Nov 14 '19 at 15:29
mathlab does not require data in scientific notation. you'll get scientific notation by default for any numbers which are too large to display fully — Klaycon, Nov 14 '19 at 15:37

Jon Skeet · Accepted Answer · 2019-11-14T15:28:39.493

You're explicitly formatting the values. Don't do that - add the elements directly to the array:

if (value is List<double> myList)
{
    JArray myArray = new JArray();
    foreach (var element in myList)
    {
        myArray.Add(element);
    }
    myArray.WriteTo(writer);
}

Or write directly to the writer:

if (value is List<double> myList)
{
    writer.WriteStartArray();
    foreach (var element in myList)
    {
        writer.WriteValue(element);
    }
    writer.WriteEndArray();
}

This may not get to the exact representation you want (in terms of scientific notation), but it will get to a valid JSON representation of the data you're trying to serialize. Anything reading the JSON should be able to read the exact same value from the JSON.

If you absolutely have to customize the format, you can use JsonWriter.WriteRawValue, using the invariant culture to format your values. But I'd strongly advise you not to. I'd be really surprised at a JSON parser that can't handle the regular output of Json.NET. Here's a complete example if you really, really have to do it:

using System;
using System.Globalization;
using System.Collections.Generic;
using Newtonsoft.Json;

class Program
{    
    static void Main(string[] args)
    {
        var writer = new JsonTextWriter(Console.Out);
        var list = new List<double>
        {
            -9.811880E-002,
            2.236657E-002,
            -4.020144E-001
        };
        WriteList(writer, list);
    }

    static void WriteList(JsonWriter writer, List<double> list)
    {
        writer.WriteStartArray();
        foreach (var element in list)
        {
            writer.WriteRawValue(element.ToString("E", CultureInfo.InvariantCulture));
        }
        writer.WriteEndArray();
    }
}

Output:

[-9.811880E-002,2.236657E-002,-4.020144E-001]

@Juri: No, but it will give you valid JSON which can be read by any JSON parser to give the right result. What is your reason for needing scientific notation? — Jon Skeet, Nov 14 '19 at 15:22
@Juri: I'll see whether I can write some code to do that, but I would *strongly* suggest that you don't use it. The more "customized" your serialization is, the more likely it is you'll end up with a bug in it. — Jon Skeet, Nov 14 '19 at 15:24
@Juri: Are you saying MathLab can't parse the standard JSON created by Json.NET? That would seem highly odd. — Jon Skeet, Nov 14 '19 at 15:27
@Juri: I've added a way of serializing to scientific notation, but as I say, I'd be really surprised if you actually needed it. — Jon Skeet, Nov 14 '19 at 15:29

score 0 · Answer 2 · answered Nov 14 '19 at 15:10

0

You're doing dblValue.ToString("E") which is why you're getting strings.

answered Nov 14 '19 at 15:10

Soham Dasgupta

5,061
24
79
125

1

yes, this is the reason - but what is the solution? – Juri Nov 14 '19 at 15:12
What happens if you remove it? – Soham Dasgupta Nov 14 '19 at 15:13
i will get a double (with no quote) but not in scientific notation :-/ – Juri Nov 14 '19 at 15:16
1

@Juri I'm not sure how you would expect this to be solved. Scientific notation is a domain concept, not a datatype. If you want SN then it's a string. If you want just the value, then it's a double. Where lies the problem with a string or an actual double? – Austin T French Nov 14 '19 at 15:20

nzrytmn · Answer 3 · 2019-11-14T15:25:49.640

0

JArray.Add except Object too as argument. So, you don't have to convert your double to string. Just directly add to array.

Have a look here for details.

edited Nov 14 '19 at 15:25

answered Nov 14 '19 at 15:18

nzrytmn

6,193
1
41
38

this wil not give me the scientific notation – Juri Nov 14 '19 at 15:21

How to write List to Json in scientific notation in c#?

3 Answers3