plotting data from two years with day of year replacing julian date

I have the following code for producing a plot of data that extends two years in terms of day of year:

time = datenum('2008-04-17 02:00'):datenum('2009-11-24 12:27');
dateV = datevec(time);
for i = 1:length(time);
    DOY(i) = time(i) - datenum(dateV(i,1),0,0);
end
data = rand(length(time),1);
plot(time,data);
set(gca,'XTick',floor(time(1:50:end))','XTickLabel',floor(DOY(1:50:end)))

Could someone suggest a method for ensuring the ticks on the xaxis are for day numbers that are multiples of 10 i.e. 110, 160 etc.

Answer 1

[Star Strider]

Does this do what you want (placed after your for looop)?

data = rand(length(time),1) + sin(2*pi*DOY'/365)/5;

StartDOY = 200;
InitDOYIdx = find(DOY >= StartDOY, 1, 'first')
PlotIdx = [InitDOYIdx:length(DOY)]';

plot(time(PlotIdx),data(PlotIdx));

xtiklocs = floor(time(InitDOYIdx:50:end))';
xtiklbls = 10*floor(DOY(InitDOYIdx:50:end)/10)';

set(gca,'XTick',xtiklocs,'XTickLabel',xtiklbls)

Produces:

    Dates          xtiklocs       xtiklbls
  2008 07 18    733607    200
  2008 09 06    733657    250
  2008 10 26    733707    300
  2008 12 15    733757    350
  2009 02 03    733807     30
  2009 03 25    733857     80
  2009 05 14    733907    130
  2009 07 03    733957    180
  2009 08 22    734007    230
  2009 10 11    734057    280

I changed data a bit to provide a trend as a check to be sure different start times plotted appropriately. (I set it arbitrarily to start at the beginning of 2008.)

I broke out ‘xtiklocs’ and ‘xtiklbls’ as separate variables so I could keep track of them, and coded ‘xtiklbls’ to produce only multiples of 10, as you requested.

I made ‘InitDOYIdx’ the index of the first occurrence of the 200th day because you asked for that as an illustration. You can of course define it with ‘StartDOY’ to be any ‘DOY’ index that works with your data.

Answer 2

[Azzi Abdelmalek]

close
time = datenum('2008-04-17 02:00'):datenum('2009-11-24 12:27');
dateV = datevec(time);
for i = 1:length(time);
  DOY(i) = time(i) - datenum(dateV(i,1),0,0);
end
data = rand(length(time),1);
n=length(time)
plot(1:n,data);
set(gca,'XTick',10:50:n)

[Richard]

Is there an alternative method? Without specifying 10 and 50, maybe from DOY?

[Azzi Abdelmalek]

what do you want exactly on x axis

[Richard]

The code you have shown works fine for that particular example, but the xaxis is for DOY so say if my data was from day 200 (as given by the Julian date ('time')) then the axis you have shown would not be useful.

[Azzi Abdelmalek]

when you say 200, compared to what, what is your mark? how can we know that is 200, then we can fix our code

[Richard]

So, the original time series is for julian date, I want to show the xaxis as day of year so I calculate 'DOY'. I then plot the data against julian date ('time') and then convert the xaxis to DOY. The day number therefore depends on the original time vector (of julian dates) which could start on any day of the year (50,200,250 and so on). Basically instead of the code you have provided above I was looking for a solution that moved the xticks to the location where the first DOY was a multiple of 10 and then did the same for the remaining ticks. Hope this makes sense.