How can I sort data in a loop with an if selection structure?

Question

Michael Toney 2014-10-21

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回答： Mohammad Abouali 2014-10-22

Say if I have a vector of numbers grades = [84;62;91;85;73;69;44;90;82] and I want to sort them like grades, A being 90-100, B being 80-89, C being 70-79, D being 60-69, and F below 60. I want to use a loop with an if selection structure to sort them. But when I run my code only my F values show up with a column vector of zeros and 1's being in place of the values that are true for the F grades. Any suggestions on how to correctly do this?

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Michael Toney 2014-10-21

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Here is what I have, NOTE: The grades are different than the question stated, this being my work. But I want to incorporate a while loop in the code, but could not figure out a condition to make it run considering its only taking the data once through for ever condition.

if grades >= 93     
      A2 = find(grades >= 93)     
  elseif grades >= 90 & grades < 93    
      A_m2 = find(grades >= 90 & grades < 93)     
  elseif grades >= 87 & grades < 90       
      B_p2 = find(grades >= 87 & grades < 90)       
  elseif grades grades >= 83 & grades < 87     
      B2 = find(grades >= 83 & grades < 87)      
  elseif grades >= 80 & grades < 83     
      B_m2 = find(grades >= 80 & grades < 83)     
  elseif grades >= 77 & grades < 80 
      C_p2 = find(grades >= 77 & grades < 80)
  elseif grades >= 70 & grades < 77
      C2 = find(grades >= 70 & grades < 77)     
  elseif grades >= 60 & grades < 70     
      D2 = find(grades >= 60 & grades < 70)      
  else grades < 60    
      F2 = find(grades < 60)
  end

Amit Varshney 2014-10-21

You do need the 'if' and 'elseif' statements. Try the following

A2 = grades(find(grades >= 93))

A_m2 = grades(find(grades >= 90 & grades < 93))

ans so on..

Michael Toney 2014-10-21

I got it! I just initiated a while loop with i = 1 and after every if/elseif/else statment with i == 1, i ==2, all the way to i == 9 for the else statement. Then after finding the grades I just did i = i + 1 that way it would go to the next statement. After F2 I just put i = 0 so the loop would terminate.

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Answer 1

Mohammad Abouali 2014-10-22

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Another way of coding without all these if then classes is this:

% Generating some random grades
Grades_Numeric=randi(100,[10,1]);
levels=[60,70,77,80,83,87,90,93,97];
GradesClasses={'F';'D';'C';'C+';'B-';'B';'B+';'A-';'A';'A+'};
% now getting each grade falls in what category
Grades_Mask=imquantize(Grades_Numeric,levels);
[Grades_Mask Grades_Numeric]
ans =
       2    66
       1    50
       4    78
       3    72
       8    91
       7    90
       1    34
       2    70
       1    20
       1     4
%retrieving the categorial grades.
GradesClasses(Grades_Mask)
ans = 
      'D'
      'F'
      'C+'
      'C'
      'A-'
      'B+'
      'F'
      'D'
      'F'
      'F'

The good thing about this approach is that if you want to change your levels and classes you don't need to write any code, (may be not in this case) but in cases that these classes and levels are not decided they can be easily passed as an input to a function.