How do I save the output from a double for loop to a vector?

Hi all,

I am trying to use a double for loop to count the number of patients admitted to a hospital (from a data set in excel) during each of the 24 hours in a day. I believe that the for loops are correct but I am unsure as to how I save the outputs (number of patients admitted each hour) in a vector?

counter = 0;
for n = 0:23
    
    for i = 1:height(Exceldata)
        if (duration(n,0,0) <= NUM_Time_Data(i)) & (NUM_Time_Data(i) <= duration(n,59,0))
            counter = counter + 1;
        end
    end
    VectorOfValues(n) = counter;
end

Answer 1

[dpb]

counter = 0;
VectorOfValues=zeros(24,1);     % preallocate
for n = 0:23
  for i = 1:height(Exceldata)
    if (duration(n,0,0) <= NUM_Time_Data(i)) & (NUM_Time_Data(i) <= duration(n,59,0))
      counter = counter + 1;
    end
  end
  VectorOfValues(n+1) = counter;
end

But, "the MATLAB way" to do this will eliminate both loops -- use histcounts or, better yet, put the Excel data into a Matlab table and use groupsummary with the time data turned into datetime or timeofday class. See the general doc on tables and processing by grouping variables; it'll be a big timesaver in the long run compared to going at it brute force for every little detail.

[matt beemsterboer]

For my purposes, the counter must be within the first loop, not outside both of them. But I forgot that I had to preallocate an array of a certain size. Thank you for that.

[dpb]

Still, it would be far better to load the data into a more useful form for analyses...

tPatients=table(datetime(2020,randi([1 12],1000,1),randi([0 23],1000,1)), ...
                hours(randi([0 23],1000,1))+minutes(randi([0 59],1000,1)), ...
                'VariableNames',{'AdmittingDate','AdmittingTime'});
tPatients=sortrows(tPatients,{'AdmittingDate','AdmittingTime'});
tPatients.AdmittingTime.Format='hh:mm';
head(tPatients)

    AdmittingDate    AdmittingTime
    _____________    _____________

     31-Dec-2019         00:35    
     31-Dec-2019         01:49    
     31-Dec-2019         02:32    
     01-Jan-2020         14:59    
     01-Jan-2020         19:45    
     02-Jan-2020         01:29    
     02-Jan-2020         10:09    
     02-Jan-2020         10:59    

groupcounts(tPatients,'AdmittingTime','hour')

ans = 24×3 table
    hour_AdmittingTime    GroupCount    Percent
    __________________    __________    _______

      [00:00, 01:00)          33          3.3  
      [01:00, 02:00)          47          4.7  
      [02:00, 03:00)          50            5  
      [03:00, 04:00)          43          4.3  
      [04:00, 05:00)          43          4.3  
      [05:00, 06:00)          47          4.7  
      [06:00, 07:00)          26          2.6  
      [07:00, 08:00)          39          3.9  
      [08:00, 09:00)          49          4.9  
      [09:00, 10:00)          40            4  
      [10:00, 11:00)          56          5.6  
      [11:00, 12:00)          33          3.3  
      [12:00, 13:00)          43          4.3  
      [13:00, 14:00)          46          4.6  
      [14:00, 15:00)          33          3.3  
      [15:00, 16:00)          53          5.3