How do I match two arrays in C# like in Javascript?

Question

To make sure two arrays are the same in Javascript, this is what I do: (inserting zeroes where there is missing data in item1)

    var viewModel = @Html.Raw(Json.Encode(Model));
    var items = viewModel.Date1;
    var items2 = viewModel.Date2;

    items = items2.map( row => 
        //is there a matching row in items?
        items.filter( r => r.theString == row.theString).length ==  0 ? 
       //if not, fill with zeros
              {theString:0, theCount:0} : 
       //if there is, return the items' row
       items.filter( r => r.theString == row.theString)[0] );

I use that data for the barchart as percentages. I need to display the results in table form with the actual count numbers like this:

<div style="padding-top: 30px">
    <table id="table_id" class="display">
        <thead>
            <tr>
                <th>Month</th>
                <th>Cancelled</th>
                <th>Total</th>
            </tr>
        </thead>
        <tbody>
            @using (var e1 = Model.Date1.Reverse().GetEnumerator())
            {
                using (var e2 = Model.Date2.Reverse().GetEnumerator())
                {
                    while (e1.MoveNext() && e2.MoveNext())
                    {
                        var item1 = e1.Current;
                        var item2 = e2.Current;
                        <tr>
                            <td>@item1.theDate.Value.ToString("MMMM-yyyy") </td>
                            <td>@item1.theCount</td>
                            <td>@item2.theCount</td>
                        </tr>
                    }
                }
            }
        </tbody>
    </table>
    </div>

Problem is that those arrays haven't been fixed to match eachother, so the data it's displaying is incorrect. The dates (theDate) are not matching the values.

Or could I just use items and items2 from the javascript to make a table?

I would infinitely prefer to have one array of tuples/objects/whatever than two parallel arrays of things that are supposed to match up at the same index. For this reason, and because it would massively clean up the loop in your razor code, and... you name it. — 15ee8f99-57ff-4f92-890c-b56153
– 15ee8f99-57ff-4f92-890c-b56153, Commented Sep 22, 2016 at 15:33
I don't know what Type (class) item1 nor item2 are so I don't know how to compare them to know if they are the same or not. Otherwise, using Linq's Lambda methods like Zip(), Where() and Select() can create a single list to loop through without all the old school GetEnumerator() and MoveNext() methods that aren't necessary in current .Net versions. — Erik Philips
– Erik Philips, Commented Sep 22, 2016 at 15:39
Have you looked into Linq's .Select method? It should be functionally similar to .map. msdn.microsoft.com/en-us/library/bb534869(v=vs.110).aspx — Simon Ordo
– Simon Ordo, Commented Sep 22, 2016 at 15:52
@ErikPhilips They are exactly the same, with different values (one is the total). — Stem Step
– Stem Step, Commented Sep 22, 2016 at 16:07

StriplingWarrior · Accepted Answer · 2016-09-22 16:07:28Z

Something like this should work:

@foreach (var item1 in Model.Date1.Reverse())
{
    var item2Count = Model.Date2.Where(i2 => i2.theDate == item1.theDate)
        .Select(i2 => i2.theCount)
        .FirstOrDefault();
    <tr>
        <td>@item1.theDate.Value.ToString("MMMM-yyyy") </td>
        <td>@item1.theCount</td>
        <td>@item2Count</td>
    </tr>
}

This has the same n² asymptotic complexity as the JavaScript you posted, so if you had a very large number of items there's a chance you'd see slow performance. This could be resolved by creating a lookup of the Date2 values, like so:

@{
var item2CountsByDate = Model.Date2.ToLookup(i => i.theDate, i => i.theCount);
foreach (var item1 in Model.Date1.Reverse())
{
    var item2Count = item2CountsByDate[item1.theDate]
        .FirstOrDefault();
    <tr>
        <td>@item1.theDate.Value.ToString("MMMM-yyyy") </td>
        <td>@item1.theCount</td>
        <td>@item2Count</td>
    </tr>
}
}

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