yogi_Sort First And Last Name Columns Then Merge Them As LastName comma FirstName

Yogi Anand, D.Eng, P.E.                                         Google Spreadsheet                            www.energyefficientbuild.com
user lalunaselena said:
How do I sort First & Last name columns, joining to one cell in third column

First     |    Last     | Sorted

Sammy     |    Sue      |

Sally     |    Sue      |  

John      |    Smith    |  

Jane      |    Doe      |

I've got three columns: First name, Last name, Sorted Names. I want to sort by Last, then First, then join First & Last column and report in alphabetical order in Sorted column. I have gotten as far as this: =arrayformula(sort(D2:D)&", "&_____) I want Sorted to report: 

Doe, Jane

Smith, John

Sue, Sally

Sue, Sammy

I don't know how to get it to sort second priority by First column. If I do =arrayformula(sort(D2:D)&", "&sort(C2:C)), it sorts last name and outputs that, then it sorts first name and outputs that, but then the first and last names are mismatched. e.g. Sue, Jane

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following is a solution to the problem: