Include missing elements in array (matlab)

I have a Matlab table called 'mytable' with two columns (Times and value). See example extract below:

I would like to detect and include the missing time stamps in the Times column and assign an empty value in the following way:

I have only figured out how to do it using the following code:

%%Creates a complete duration array
A=duration(00,00,00);
B=duration(23,59,59);
Complete_time_array=linspace(A,B,86400);

%%Compare Complete_time_array with mytable.Times values and include the missing time stamps
Times=repmat({''},length(Complete_time_array),1);
value=repmat({''},length(Complete_time_array),1);

for t=1:length(Complete_time_array)
  if any(strcmp(char(Complete_time_array(1,t)),mytable.Times))==1
      index=find(strcmp(char(Complete_time_array(1,t)),mytable.Times));
              Times{t,1}=mytable.Times(index,1); 
              value{t,1}=mytable.value{index,1};     
  else
    Times{t,1}=char(Complete_time_array(1,t)); 
    value{t,1}='';   
  end
end

mynewtable=table(Times,value);

However, when working with tables that have thousands of rows, this code takes too long despite having used the 'any' and 'find' matlab functions. Does anybody know how to achieve this goal more efficiently?

Answer 1

[Madhav Rajan]

I understand that you want to include the missing timestamps using [] in your newtable. You can make use of the 'intersect' function to compare the durations in the complete time array with the durations in your table. You can use the below example for your reference:

%%Initalization 
%  This creates the Time and values array
times = duration(0, 1, 0:20)';
vals = rand(21,1);

Perform intersection with the new duration variable

newtimes = duration(0, 0, 0:120)';
result = cell(length(newtimes),1);

%get the duration, the duration's index in times and the duration's index
%in newtimes
[dur, itimes, inewtimes ] = intersect(times,newtimes);

v=num2cell(vals(itimes));
[result{inewtimes}] = deal(v{:});

newtable = table(newtimes, result);

In the above example the first section initializes the times and vals similar to your 'mytable'. The second section creates an array of newtimes which contains more duration values than the first times variable. You then find the intersection and its indices between the two time variables and then assign the values to the corresponding indices in the newtimes variable. With the indices available, you would just have to do a cell array assignment as shown above.

You can refer the following link for more information on the 'intersection' function:

http://www.mathworks.com/help/matlab/ref/intersect.html

Hope this helps.

[Nia]

Thanks!, it worked. But in my case as I had a cell array and a duration array, I also had to convert my Complete_time_array duration array into a cell array to be able to use the intersect function:

     b=char(Complete_time_array);
     [dur, itimes, inewtimes ] = intersect(mytable.Times,b);

Otherwise I was getting the following error: "Error using duration/intersect. Comparison is not defined between cell and duration arrays". I think both elements must be of the same class before they can be intersected.