% Use a uniform distribution to choose students at random 
% We will generate code for sampling students at random
%  There are ? students...
%    we divide the space between 0 and 1 into equal intervals and mark them

names=['Antonio   '
       'Carlos    '
       'Carolina  '
       'CristianeC'
       'CristianeJ'
       'Bia       '
       'Maria     '
       'Rosa      '
       'MauricioB '
       'Rita      '
       'Talita    '
       'Daniela   '
       'MauricioC '
       'Vania     '
       'Flavia    '
       'Luciano   '
       'Silvana   '];
 
dimnames=size(names);                    %dimensions of names matrix 
nnames=dimnames(1);                      %no. of rows in names matrix, what does this tell us?
marks=linspace(0,1,nnames+1);            %we want n+1 marks from 0 to 1
marks1=marks(1:nnames);                  %start with 0, end before 1
marks1=marks1';
matches=[names num2str(marks1)];         %turn the numerical marks into character "strings"
matches                                  %learn your interval... this is the lower bound of it

        

%imagine that the 20 random numbers are drawn... 
% who will be called on?
T=20 %length of loop, %try this again with 200, and then with 2000

rand('state',sum(100*clock)) %reseeds the random number generator

%loop to choose random numbers and set up matrix to receive chosen students
for i=1:T
X = rand(1,T);
students= char(zeros(i,dimnames(2))); % make it a character array i rows, same length as "names"
end;

%loop to choose students
for i=1:T;
   j = min(find(marks > X(i))); %get ith random number and decide which student it corresponds to
                                 % find the _first_ time along the line a particular mark is greater than the random number                  
   student = names(j-1,:);        % go back one: that is the student whose segment it is
   students(i,:)=student;        %put the student into the sequence of chosen ones
 end;
 
    students                    % here is the sequence chosen at random
    
%make a plot of the frequency distribution of chosen ones
spacesshift=marks(2:nnames+1);             %find midpoints step 1
midspaces=(marks(1:nnames)+spacesshift)/2; %find midpoints step 2

n=hist(X(2:T),midspaces)   %for T  don't include the first element which is 0, number of bins equals number of students
figure(1)
subplot(2,1,1)
bar(n)
subplot(2,1,2)
hist(X(2:T),midspaces)   %for T don't include the first element which is 0, number of bins equals number of students
axis([0 1 0 max(n+1)])   % set the y-axis according the maximum observed frequency
xvalues=names;
set(gca,'XTick',[midspaces],'FontName','Helvetica','FontSize',6)
set(gca,'XTickLabel',{xvalues},'FontName','Helvetica','FontSize',6)