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

3 views (last 30 days)
Kendra Wright on 24 Nov 2014
Commented: Star Strider on 24 Nov 2014
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.

Star Strider on 24 Nov 2014
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.
Kendra Wright on 24 Nov 2014
I felt like this was an option but I just couldn't find that in the documentation. Thanks
Star Strider on 24 Nov 2014
My pleasure!

Andrew Reibold on 24 Nov 2014
Edited: Andrew Reibold on 24 Nov 2014
I'm really confused as to why you have Data{1,3}{i,1} for the first assignment, and Data{3,i}{i,1} for the second one. Shouldn't these both be the same? Could this be your issue?
Also, maybe try entering your numbers as STRINGS. Use the parenthesis.
Also, you can put strcmp directly into the if statement if that helps you clean stuff up.
Here is an example. You may need to tune it up.
for i=1:l3
if strcmp(Data{1,3}{i,1},'AM')
Data{1,3}{i,1} = '0';
else if strcmp(Data{1,3}{i,1},'PM')
Data{1,3}{i,1} = '12'
end

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