A “Select” Algorithm for Cell Array Databases

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• Misc
  • Exam 2 solution is online via “Exercises” page
  • Final
    • Tuesday, May 12, 8:00 AM
    • Comprehensive, but emphasizing material since 2nd hour exam (e.g., cell arrays, strings, files, etc.)
    • Designed for 2 hours, you’ll have 3
    • Otherwise similar rules and format to hour exams
    • Donuts and cider
  • SOFIs
    • Fill them out via http://go.geneseo.edu/sofi_survey
    • Useful to me in improving courses
• Questions?
• Relations and Cell Arrays
  • Selection algorithm
    • Examples:
      • Select ‘Isaac Newton’ in column 1 (name attribute) from mathContributions relation
        • Result: cell array with 1 row
          

          Isaac Newton, Calculus, 1667

      • Select ‘Calculus’ in column 2 (contribution attribute) from mathContributions relation
        • Result: 2 rows
          

          Newton, Calc, 1667
          Leibniz, Calc, 16??

      • Select ‘Isaac Newton’ in column 1 of csContributions
        • Result: empty cell array
    • Algorithm version 1
      

      select( value, column, relation )
          Go down every row of relation and check for value in column
          When you get to row with that value in that column, put it in new relation
          (Output is new relation)

    • Algorithm version 2
      

      function result = select( value, column, relation )
          n = number of rows in relation
          result = empty cell array
          count = 1
          for i = 1 to n
              if relation{i,column} == value
                  result(count,:) = relation(i,:)
                  count = count + 1

  • Equality tests in this (and union) need to compare multiple types of value
    • Use isequal to do this
      

      >> isequal( 2, 2 )
      ans =
           1
      >> isequal( 'foo', 'hello' )
      ans =
           0
      >> isequal( 'foo', 'foo' )
      ans =
           1
      >> isequal( 1, 'hello' )
      ans =
           0

• Next
  • Union algorithm
  • Extend grading date for relations lab to Thursday, May 7

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