Concatinating properties in a list of items

I am having trouble with a small section of code.

I have a List of a MapItem class with a couple properties, Address and Html, and I need to concatenate the Html properties for each item with an identica开发者_如何转开发l Address property For example:

firstMapItem = new MapItem { Address = "1122 Elm Street", 
                             Html="<p>some html</p>" };  
secondMapItem = new MapItem { Address = "1122 Elm Street", 
                              Html="<p>different html</p>" };

would become:

firstMapItem.Address == "1122 Elm Street";
firstMapItem.Html == "<p>some html</p><p>different html</p>";

secondMapItem.Address == "1122 Elm Street"; 
secondMapItem.Html == "<p>some html</p><p>different html</p>";

This is what I have tried so far:

            foreach (MapItem item in mapItems)
            {
                var sameAddress = from m in mapItems
                                  where m.Address == item.Address
                                  select m;

                if (sameAddress.Count() > 1)
                {
                    //tried inserting -> item.Html = ""; right here as well
                    foreach (MapItem single in sameAddress)
                    {
                        item.Html += single.Html;
                    }
                }
            }

I am probably making this more complicated than it needs to be.

Thanks in advance.

---

You could group by Address and then concatenate the Html values:

var results = from m in mapItems
              group m by m.Address into ms
              select new MapItem
              {
                  Address = ms.Key,
                  Html = string.Concat(ms.Select(m => m.Html))
              };

---

Use a grouping on the address, then just string.Join the Html of all the items in the group to produce a new MapItem:

var resultList = mapItems.GroupBy(m => m.Address)
                         .Select(g => new MapItem() { Address = g.Key, Html = string.Join("", g.Select(x => x.Html)) })
                         .ToList();

Edit:

Like the other solutions presented so far above approach will remove duplicates - that doesn't seem to be what you want - below a solution that creates a list that is not deduplicated (so will produce 2 items for the sample input)

var resultList = mapItems.GroupBy(m => m.Address)
                         .Select(g => g.Select( item => new MapItem() { Address = g.Key, Html = string.Join("", g.Select(x => x.Html)) } ))
                         .SelectMany( x=> x)
                         .ToList();

---

If you group by Address, you'll end up with only one item when you have items with the same Address. If that's OK with, go with Group By. However, if you need all the original items, with the Html concatenated, you should do like that:

var newMapItems = mapItems
    .Select(mi => new MapItem() { Address = mi.Address, 
                                  Html = mapItems.Where(mi2 => mi2.Address == mi.Address)
                                                 .Select(mi3 => mi3.Html)
                                                 .Aggregate((acc, html) => acc += html) 
                                }
           );

---

You can do this with a GroupBy and Select:

    var result = items
        .GroupBy(m => m.Address, m => m.Html)
        .Select(g => new MapItem() {Address = g.Key, Html = string.Concat(g.Select(h => h))});

---

This code should update your existing objects with appended values.

foreach (MapItem item in mapItems)
            {

                var sameAddress = from m in mapItems
                                  group m by m.Address into ms
                                  select string.Join("", ms.Select(e => e.Html).ToArray());

                foreach (string concatHtml in sameAddress)
                {
                    item.Html = concatHtml;
                }

            }