Comparing Possibly Dissimilar Values

Return to List of Lectures

Previous Lecture

• Misc
  • SOFIs
    • http://go.geneseo.edu/sofi_survey
  • Final Exam
    • Wednesday, Dec. 10, 8:00 AM
    • Comprehensive but emphasizing material since 2nd hour exam (e.g., cell arrays, files, strings)
    • Designed for 2 hours, you’ll have 3
    • Otherwise similar rules and format to hour exams, esp. open references and computers
    • Donuts and cider
• Questions?
• Relations Lab
  • Remember “grade by” date is now Wednesday Dec. 10
  • Comparisons
    • “Select” algorithm uses comparison R(i,c) == v
    • Awkward in Matlab because of possibly different sizes of v and elements from R
    • Solutions?
      • Are lengths equal? and if so, are values equal?
      • Equivalently, “if lengths are equal and values are equal...”
        

        >> name = 'Isaac Newton';
        >> number = 3;
        >> name == number
        ans =
            Columns 1 through 10
              0     0     0     0     0     0     0     0     0     0
            Columns 11 through 12
              0     0
        >> name2 = 'Alan Turing';
        >> name == name2
        {Error using  == 
        Matrix dimensions must agree.
        } 
        >> strcmp(name,name2)
        ans =
            0
        >> name3 = 'Isaac Newton';
        >> strcmp(name,name3)
        ans =
            1
        >> strcmp(number,3)
        ans =
            0
        >> number
        number =
            3
        >> cmp = @(x,y) length(x) == length(y) && x == y
        cmp = 
            @(x,y)length(x)==length(y)&&x==y
        >> cmp(name,name2)
        ans =
            0
        >> cmp(name,number)
        ans =
            0
        >> cmp(name,name3)
        {Operands to the || and && operators must be convertible to
        logical scalar values.
        Error in @(x,y)length(x)==length(y)&&x==y
        } 
        >> name3
        name3 =
        Isaac Newton
        >> name
        name =
        Isaac Newton
        >> name == name3
        ans =
            Columns 1 through 9
              1     1     1     1     1     1     1     1     1
            Columns 10 through 12
              1     1     1
        >> all(name==name3)
        ans =
            1
        >> cmp = @(x,y) length(x)==length(y) && all(x==y)
        cmp = 
            @(x,y)length(x)==length(y)&&all(x==y)
        >> cmp(name,name3)
        ans =
            1
        >> cmp(name,name2)
        ans =
            0
        >> cmp(name,number)
        ans =
            0
        >> isequal(name,name2)
        ans =
            0
        >> isequal(name,name3)
        ans =
            1
        >> isequal(name,number)
        ans =
            0

• Work on lab (or Madlibs project)
  • Note that digit characters and numbers are not equal!
    

    >> number
    number =
        3
    >> cmp(number,'3')
    ans =
        0
    >> cmp(3,'3')
    ans =
        0
    >> length('3')
    ans =
        1
    >> length(3)
    ans =
        1

• Next
  • Finish lab, ask Mad Lib questions, etc.

Next Lecture