LINQ：如何使用单行链式 SelectMany 或嵌套式 SelectMany 将结构结构展平为一个线性结果？

Question

I have an array of struct _LOC of array of struct _FAC of array of values!!!

  private static List<_LOC> _m_Locs { get; set; }
  private struct _LOC {
     public string key;
     public List<_FAC> _facs;
  }
  private struct _FAC      {
     public string key;
     public List<int> _vals; 
  }

My _m_Locs[i].key can contain any of these==> string[]{"AA", "BB", "CC"};
My _m_Locs[i]._facs[j].key can contain any of these==> string[]{"F1", "F2", "F3"}.

Each _m_Locs[i]._facs[j] has 21 integer values!

Now, I want to have flat linear results --

List<string, string, int> as of iterating _m_Locs thru i,j,k's

to output (_loc[i].key, _loc[i]._fac[j].key, _loc[i]._fac[j]._vals[k]).

Answer 1

There are two solutions:

1. Chained SelectMany's; That is, selectMany(x=>xy).SelectMany(xy=>xy.zz)
2. Nested SelectMany's; That is, Select Many(x=>xySelectMany(y=>y.values)),

In this case, the Nested SelectMany solution is:

var soln1 = _m_Locs
           .SelectMany(
            lcn => lcn._facs.SelectMany(
            ff => ff._vals, (ff, vv) => new { loc=lcn.key, fac=ff.key, value=vv }));

Or, you can also use Chained SelectMany:

 var soln2 = _m_Locs
.SelectMany(lcn => lcn._facs, (lcn, FF) => new { aLoc = LL.key, aFac = FF.key, vals = FF._vals })
.SelectMany(FF => FF.vals, (FF, nVal) => new { loc = FF.aLoc, fac = FF.aFac, value = nVal });

Since they both yield same result, I prefer the simpler one which is the Nested SelectMany!

Enjoy!