Issues with creating a JSON string

Question

My brain is not working and I am trying to make something harder than I think it really should be and I need another set of eyes. I have the following in a text file

|TS|170702/2300|170703/0503|42.80 -102.64 39.76 -102.64 39.44 -99.37 42.48 -99.37
|TS|170703/0505|170703/0905|40.22 -97.30 38.63 -97.30 38.19 -101.03 39.78 -101.03

what the above means...(|watchtype|watchstart|watchend| lat/long pairs)

The problem I'm having is that I need to take EACH ROW (could be 0 or could be 100+) and create a polygon on a map to mark the location of these storm watches. I currently have the following.

MODEL

public class WatchPolygons
{
    public string WatchType { get; set; }
    public string WatchStart { get; set; }
    public string WatchEnd { get; set; }
    public List<lat_longPairs> Lat_Long_Pairs {get; set;}
}

public class lat_longPairs
{
    public decimal latitude { get; set; }
    public decimal longitude { get; set; }
}

CONTROLLER

public JsonResult GetWatchPath()
{
    var watchFilePaths = ConfigurationManager.AppSettings["watchFilePath"];
    return Json(Directory.GetFiles(Server.MapPath(watchFilePaths), "current*.txt"), JsonRequestBehavior.AllowGet);
}

[HttpGet]
public ActionResult GetWatchData(string watchPath)
{
    var stringData = new List<string>();
    using (var reader = new StreamReader(watchPath))
    {
        while (!reader.EndOfStream)
        {
            var data = reader.ReadLine().Trim();

            if (!string.IsNullOrEmpty(data))
                stringData.Add(data);
        }

    }

    return Json((from item in stringData
                 select item.Split(new char [] { '|' }, StringSplitOptions.RemoveEmptyEntries)
                into rawData
                 select new WatchPolygons
                 {
                     WatchType = rawData[0],
                     WatchStart = rawData[1],
                     WatchEnd = rawData[2]
                 }).ToList(), JsonRequestBehavior.AllowGet);
}

I know I am missing the latlong pairs = rawData. I don't have it in the code because in the model it's a list and I can't easily convert the list to string the way I need it.

What am I missing? I believe I need to read over each line then read over each group to get the lat/long pairs. Just not sure.

CodeCaster · Accepted Answer · 2017-07-03 17:24:15Z

4

You just need to parse rawData[3], containing the string with space separated lat/lon pairs. This is a naive implementation that will break when the input string does not contain pairs of numbers or when the current locale doesn't use a dot as a decimal separator:

private static List<lat_longPairs> ParseLatLon(string input)
{
    var numbers = input.Split(new [] { " " }, StringSplitOptions.RemoveEmptyEntries)
                       .Select(i => decimal.Parse(i))
                       .ToArray();

    var latLonPairs = new List<lat_longPairs>();

    for (int i = 0; i < numbers.Length; i += 2)
    {
        latLonPairs.Add(new lat_longPairs
        {
            latitude = numbers[i],
            longitude = numbers[i + 1],
        });
    }

    return latLonPairs;
}

Then call it from where you're projecting the polygons:

select new WatchPolygons
{
    WatchType = rawData[0],
    WatchStart = rawData[1],
    WatchEnd = rawData[2],
    Lat_Long_Pairs = ParseLatLon(rawData[3])
}

You may want to move the parsing code away from the controller as well, into its own class.

answered Jul 3, 2017 at 17:24

CodeCaster

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2 Comments

dbc Over a year ago

There's no reason not to use decimal.Parse(i, NumberFormatInfo.InvariantInfo) to ensure consistent parsing in all cultures.

CodeCaster Over a year ago

@dbc the dot as culture-sensitive decimal separator is only one of a couple potential problems with parsing this string, as explained in this answer. It requires more error handling than just that; I wanted to show the pattern to solve this problem, not a complete, fully tested and robust solution, that's up to the reader.

William Han · Accepted Answer · 2017-07-03 19:38:41Z

You can use GroupBy since two set make a coordinate.

        var str = "|TS|170702/2300|170703/0503|42.80 -102.64 39.76 -102.64 39.44 -99.37 42.48 -99.37";  
        int itemsInGroup = 2;
        var pairs = str.Split('|')[4].Split(' ').
                    // Give each set of coordinate a group number.
                    Select((n, i) => new { GroupNumber = i / itemsInGroup, Number = n }).
                    GroupBy(n => n.GroupNumber).
                    Select(g => 
                    {
                        var coordinate = g.Select(n => n.Number).ToList();
                        return new lat_longPairs
                        {
                            latitude = decimal.Parse(coordinate[0], NumberFormatInfo.InvariantInfo),
                            longitude = decimal.Parse(coordinate[1], NumberFormatInfo.InvariantInfo),
                        };
        });

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