Converting a nested for-each to use LINQ and JOIN

Question

I have some for-each loops I am trying to convert to use LINQ with probably a JOIN I started writing it myself but couldn't quite figure it out. I have posted my half attempt too.

and I started writing it like this but couldn't quite figure our how to proceed:

Answer 1

Using SelectMany you can achieve what you want with a little bit of weirdness like the below :

var result = metaData.SelectMany(r=> myDictionary,(meta,dict)=>  dict.TryGetValue(meta.PropName,out var val) ? new { val,meta } : null)
.Where(r=> r != null || !string.IsNullOrEmpty(r.val.ToString()))
.Where(r=> r.val.GetType().IsArray ? 
       ((IEnumerable)r.val).Cast<object?>()
      .Select(v=> SomePrivateMethodCall(v, r.meta.PropertyType.GetElementType()))
                         .Any(result => !result) :
 !SomePrivateMethodCall(r.val, r.meta.PropertyType) )
.Select(r=> r.meta.PropName)).ToArray()