Accessing multiple arrays in JSON using C#

Question

My JSON looks like this:

 {"2013" : [
 { "date":"2013-01-09 12:00:00","height":0 },
 { "date":"2013-01-19 12:00:00","height":3 },
 { "date":"2013-01-29 12:00:00","height":2 }],
 "2012" : [
 { "date":"2012-02-09 12:00:00","height":0 },
 { "date":"2012-02-19 12:00:00","height":4 },
 { "date":"2012-02-29 12:00:00","height":2 }],
 "2011" : [
 { "date":"2011-03-09 12:00:00","height":3 },
 { "date":"2011-03-19 12:00:00","height":8 },
 { "date":"2011-03-29 12:00:00","height":2 }]
 }

What I am trying to do is get all of the dates and height, but I am only able to do it per year using this code:

 public class Report
 {
 public DateTime Date { get; set; }
 public int Height { get; set; }
 }
 JObject data = JObject.Parse(sr);
 var postTitles = from p in data["2013"]
 select new Report
 {
 Date = DateTime.Parse((string)p["date"]),
 Height = (int)p["height"]
 };

I was thinking of using a for loop but trying a variable inside data[" "] won't work. I was also thinking of doing var postTitles += statement but it is not allowed as well. Any ideas on how I should go about this? I am using JSON.NET and it is suggested that I do a class per year (i.e. 2013, 2012, 2011) but I want them under one class to make it easier to manipulate data.

Answer 1

I am not that great with the LINQ syntax you are using but what you want to do is create a list from many lists. So you want to use the SelectMany mapping operation from LINQ.

var postTitles = data.Children()
 .SelectMany(subitems => subitems.First)
 .Select(dataOfYear =>
 new Report
 {
 Date = DateTime.Parse((string)dataOfYear ["date"]),
 Height = (int)dataOfYear ["height"]
 }
 );

If you want only the first 100 reports of every year you could do it like this:

var postTitles = data.Children()
 .SelectMany(subitems => subitems.First)
 .Take(100)
 .Select(dataOfYear =>
 new Report
 {
 Date = DateTime.Parse((string)dataOfYear ["date"]),
 Height = (int)dataOfYear ["height"]
 }
 );

Or if you just want to free up the UI thread you could run this in a background thread:

var postTitles = await Task.Run(() => data.Children()
 .SelectMany(subitems => subitems.First)
 .Select(dataOfYear =>
 new Report
 {
 Date = DateTime.Parse((string)dataOfYear ["date"]),
 Height = (int)dataOfYear ["height"]
 }
 ));

• CCCC: Is there something missing after the "dataOfYear =>" statement?
• Mark: @CCCC sorry I used another dummy structure for testing, after loading the json data with JSON.Net I came to the same conclusion as PatrikW

Answer 2

I turned and twisted Mark's anwer somewhat and came up with this:

var postTitles = data.Children() // Select array container properties, like "2013"
 .SelectMany(x => x.First) // Select each subitem from every array
 .Select(r => // Create a report for each item
 new Report
 {
 Date = DateTime.Parse((string)r["date"]),
 Height = (int)r["height"]
 }
 );

Hopefully the inline comments will explain the logic sufficiently.

• CCCC: It did work. Thank you! Building on your question. The data is actually too large so my app suddenly lags. Say, If I am going to to choose the first 100 "Reports", will a for loop work? Because right now, I am using a a foreach (var s in postTitles) loop, using s.Date and s.Height to reference each. How would I go about it if I change it to for loop?
• Patrik Westerlund: @CCCC See Mark's updated answer for solutions to that problem.