Is there a way to compare just the time portion within a serial date number using IF statements?

Hi - is there any easy way to do a logical compare of serial date numbers of just the time portion by knowing the encoding of matlab's serial date number format? E.g. Suppose you want to get the rows of a matrix that are between 9:30am and 10:30am and you have the serial date number to work with, which contains both date and time. Is there a way to use greater than/less than symbols and perhaps applying a bit mask to do a logial IF statement against time periods you want to see in the matrix?

thank you in advance for any pointers or hints. shaun

Answer 1

[Fangjun Jiang]

Yes, I think that's the purpose of having datenum. You don't need to know the encoding at all.

StartTime=datenum(2011,11,11,09,30,00);
EndTime=datenum(2011,11,11,11,10,00);

TimeStamp=linspace(StartTime,EndTime);

A=TimeStamp>datenum(2011,11,11,11,00,00);
B=TimeStamp<datenum(2011,11,11,09,50,00);

Answer 2

[Walter Roberson]

Supposing the time to be stored in column 1 of YourRows,

timeB = (9 + 30/60)/24;
timeE = (10 + 30/60)/24;

dayfrac = mod(YourRows(:,1),1);  %important!

timeIDX = find(timeB <= dayfrac & dayfrac < timeE);