MATLAB: Replacing cells in a cell array/Dealing with AM and PM using datenum

Question

I'm creating a time stamp by converting my time and date using datenum(). Now I have the issue of the AM and PM. My thought was to run the cell array through for loop, testing to see if the string matches "PM." Which returns a 1 if true and 0 if false. Then say if it is equal to 1, force that cell in the array to equal 12, if not then equal to 0. I have a large data set right now which is made of cell arrays called Data and the third cell array is the AM and PM part. This is my code right now:

for i=1:l3
    tf = strcmp(Data{1,3}{i,1},'AM')
    if tf == 1
        Data{1,3}{i,1} = 0;
    else if tf == 1
        Data{3,i}{i,1} = 12
        end 
    end
end

It runs through the loop and tests the strings correctly but I've made an error with rewriting that array because it isn't actually changing the array. It just returns the original with the AM and PM. I want it to have either 0 or 12.

Answer 1

The datenum function can take care of the AM and PM conversions automatically if you tell it to:

DS = ['11/24/2014 9:30 AM'; '11/24/2014 9:30 PM'];
DN = datenum(DS, 'mm/dd/yyyy HH:MM AM');
DV = datevec(DN);

See formatIn under ‘Input Arguments’ for details.