C＃转换列表 <string> 到字典 <string, string> LINQ

Question

I have a JSON string[] like this : "['518','Incorrect date (it can not be earlier today or later today+1year)']" Which I deserialize using Json.Net library to a List, now I need to convert that list string to a Dictionary which key is the first value and the value is the second item in the list, following on.

I have done this using a for loop like this :

string Json = "['518','Incorrect CheckIn date (it can not be earlier today or later today+1year)']";
        var json = Newtonsoft.Json.JsonConvert.DeserializeObject<string[]>(Json);

        var errorList = new ErrorList();
        for(int i=1;i<= json.Length;i++)
        {
            errorList.ErrorMessages.Add(new ErrorMessage(){ErrorCode = json[i -1], Message = json[i]});
            i = i + 1;
        }

I was wondering is there is a way to replace the fro loop with linq.

Thanks.

Answer 1

One of the Select extensions will give you the index of the item in the enumeration. With a bit of manipulation you can group the strings together into pairs like so:

var pairs = 
    from item in json.Select((s, i) => new { index = i, value = s })
    // group by index / 2 to get pairs of values
    group item.value by item.index / 2 into grp
    // create ErrorMessage instances from the value pairs
    select new ErrorMessage { ErrorCode = grp.First(), Message = grp.Last() };

Or if you prefer fluent syntax:

var pairs = 
    json.Select((s,i) => new { s, i })
    .GroupBy(e => e.i / 2, e => e.s)
    .Select(g => new ErrorMessage{ ErrorCode = g.First(), Message = g.Last() });

Assuming your ErrorList type is derived from List<ErrorMessage> and has the AddRange method:

errorList.AddRange(pairs);

Or you could just do pairs.ToList() to get the results as List<ErrorMessage> .

Answer 2

You can try this way :

string Json = "['1','value1','2','value2','3','value3']";
var json = Newtonsoft.Json.JsonConvert.DeserializeObject<List<string>>(Json);

var result = json.Select((v, i) => new {value = v, index = i})
                 .Where(o => o.index%2 == 0)
                 .ToDictionary(o => o.value, o => json[o.index + 1]);

foreach (var pair in result)
{
    Console.WriteLine("key: {0}, value: {1}", pair.Key, pair.Value);
}