Linq IEnumerable> back to List

Question

How can I turn the following statement back to List<DocumentData>

IEnumerable<IGrouping<string, DocumentData>> documents = 
                 documentCollection.Select(d => d).GroupBy(g => g.FileName);

the goal is to get List that should be smaller than documentCollection. FileName contains duplicates so I want to make sure I don't have duplicate names.

I have also tried the following but it's still providing me with duplicate file names

documentCollection = 
    documentCollection.GroupBy(g => g.FileName).SelectMany(d => d).ToList();

This has been answered here: http://stackoverflow.com/questions/7617771/converting-from-ienumerable-to-list — BrDaHa, Jan 09 '14 at 02:15

Douglas · Accepted Answer · 2014-01-09T02:25:24.363

13

Each IGrouping<string, DocumentData> is an IEnumerable<DocumentData>, so you could simply call SelectMany to flatten the sequences:

var list = documents.SelectMany(d => d).ToList();

Edit: Per the updated question, it seems like the OP wants to select just the first document for any given filename. This can be achieved by calling First() on each IGrouping<string, DocumentData> instance:

IEnumerable<DocumentData> documents = 
    documentCollection.GroupBy(g => g.FileName, StringComparer.OrdinalIgnoreCase)
                      .Select(g => g.First())
                      .ToList();

edited Jan 09 '14 at 02:25

answered Jan 09 '14 at 02:12

Douglas

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1

@dasblinkenlight: The answer addresses the OP's current question. Its shortcomings should hopefully encourage them to refine their question. – Douglas Jan 09 '14 at 02:15
1

[MoreLINQ](https://www.nuget.org/packages/morelinq/1.0.16006) has a [`DistinctBy` method](https://code.google.com/p/morelinq/wiki/OperatorsOverview) which is worth considering here. – Preston Guillot Jan 09 '14 at 02:28

score 3 · Answer 2 · answered Jan 09 '14 at 02:14

You haven't said what T should stand for in List<T> you're looking for, so here are couple the most likely to be desired:

List<DocumentData> - rather pointless as you already have that on documentCollection
```
var results = documents.SelectMany(g => g).ToList();
```

List<KeyValuePair<string, List<DocumentData>>

var results =
       documents.Select(g => new KeyValuePair(g.Key, g.ToList())).ToList();

List<string> - just the names

var results = documents.Select(g => g.Key).ToList();

List<IGrouping<string, DocumentData>>
```
var results = documents.ToList();
```

Linq IEnumerable> back to List

2 Answers2