Simple Date Manipulations
I've recently had an opportunity to work with data for which I wanted to exclude weekend dates in order to see some trends. It took a little getting used to for me, because absolute time is not germane to the scientific and engineering data I am accustomed to.
Contents
Excel Data
I was given some data extracted from an Excel spreadsheet. Here's some of it.
mytimes = [40314.338356482 40315.334988426 40316.333935185 40316.333935237 40317.341400463 40318.336875000 40318.336875032 40318.336875295 40319.333912037 40320.337835648 40321.335960648 40322.342372685 40323.342106481 40324.335439815 40325.337696759 40326.338171033 40326.338171296 40327.340648148 40328.338912037 40329.336631944 40330.338657407 40331.337256944 40332.342314815 40333.342164352 40334.334004630 40335.341342593 40336.340104167 40338.334884259 40339.337777094 40339.337777778 40340.333842593];
As you can see, the times have a basis that is not this year! Digging around, I find I can convert these to datenum by adding a magic number. This is a conversion that you can get using the function x2mdate from Financial Toolbox.
newtimes = mytimes + 693960;
To see if this makes sense, let me extract a date string. Looking at the documentation, you can see many options for formatting the date. I have used the default setting.
lastday = datestr(newtimes(end))
lastday = 11-Jun-2010 08:00:44
I want to remove weekends from the data and only care about date, not time of day. I also want to remove duplicate dates. Let me first get the dates alone and create a unique list.
daysonly = fix(mytimes)
daysonly = 40314 40315 40316 40316 40317 40318 40318 40318 40319 40320 40321 40322 40323 40324 40325 40326 40326 40327 40328 40329 40330 40331 40332 40333 40334 40335 40336 40338 40339 40339 40340
uniquedays = unique(daysonly)
uniquedays = 40314 40315 40316 40317 40318 40319 40320 40321 40322 40323 40324 40325 40326 40327 40328 40329 40330 40331 40332 40333 40334 40335 40336 40338 40339 40340
Using another date function, I can find the days in my data corresponding to Saturday and Sunday, weekend days in the US.
n = weekday(uniquedays);
Find Saturday and Sunday.
weekends = find(n==1 | n==7);
% Remove weekend days.
myweekdays = uniquedays;
myweekdays(weekends) = [];
You can see I've deleted 7 dates from my unique list, corresponding to the weekend days.
whos
Name Size Bytes Class Attributes daysonly 31x1 248 double lastday 1x20 40 char mytimes 31x1 248 double myweekdays 18x1 144 double n 26x1 208 double newtimes 31x1 248 double s 18x3 108 char uniquedays 26x1 208 double weekends 8x1 64 double
I can check that the days I have left are weekdays.
[n,s] = weekday(myweekdays,'short');
s
s = Mon Tue Wed Thu Fri Mon Tue Wed Thu Fri Mon Tue Wed Thu Fri Tue Wed Thu
More Date Tools
Another date tool you might find useful is the function datetick, for labeling plots. For more on dates in MATLAB, check out the documentation.
I am curious how many people have data, other than financial data, where the actual date, rather than a relative one, is important to your data analysis. Let me know here.
- カテゴリ:
- Less Used Functionality
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