IDictionary<string, IDictionary<string, ICollection<string>>> To LINQ - c#-4.0

Question

I'm have been trying to convert the foreach statement below to a LINQ statement but can't seem to wrap my head around it. Any help would be welcome.
IDictionary<string, IDictionary<string, ICollection<string>>> Highlights { get; set; }
foreach (var r in matchingProducts.Highlights)
{
string szKey = r.Key;
var ar = r.Value.ToArray();
foreach (var s in ar)
{
string szCat = s.Key;
var sr = s.Value.ToArray();
foreach (var t in sr)
{
string szName = t;
//todo: update the corresponding matchingProduct records
// using the return values from szKey, szCat, szName
}
}
}
matchingProducts
public class Product {
[SolrUniqueKey("id")]
public string Id { get; set; }
[SolrField("sku")]
public string SKU { get; set; }
[SolrField("name")]
public string Name { get; set; }
[SolrField("manu_exact")]
public string Manufacturer { get; set; }
[SolrField("cat")]
public ICollection<string> Categories { get; set; }
[SolrField("features")]
public ICollection<string> Features { get; set; }
[SolrField("price")]
public decimal Price { get; set; }
[SolrField("popularity")]
public int Popularity { get; set; }
[SolrField("inStock")]
public bool InStock { get; set; }
[SolrField("timestamp")]
public DateTime Timestamp { get; set; }
[SolrField("weight")]
public double? Weight { get; set;}
}

Answer 1

You could just enumerate the following LINQ query
var query = from r in Highlights
let szKey = r.Key
let szValue = r.Value
from s in szValue
let szCat = s.Key
let sr = s.Value
from t in sr
let szText = t
select new { Key = szKey, Category = szCat, Text = szText };
// or, also, you can use this small query
var query = from r in Highlights
from s in r.Value
from t in s.Value
select new {Key = r.Key, Category = s.Key, Text = t};
foreach(var element in query)
{
ProcessUpdate(element.Key, element.Category, element.Text);
}

Answer 2

You can flatten the dictionary to the items in the innermost collection by writing
dict.Values.SelectMany(d => d.Values).SelectMany(c => c)
In these lambda expressions, d is the inner dictionary, and c is the innermost ICollection.
You can get the outer keys like this:
dict.SelectMany(kvpOuter =>
kvpOuter.Value.SelectMany(kvpInner =>
kvpInner.Value.Select(item =>
new {
OuterKey = kvpOuter.Key,
InnerKey = kvpInner.Key,
Item = item,
}
)
)
)