Creating variable averaged over two strata

Hi there,

I have a two long variables (+40,000 measures) of doubles x & y and i would like to calculate a third variable from them z. However X and Y are measured over time and at various depths in the ocean, not always at the same exact depths so in order to calculate my z variable i need to do some matlab wizardry?? (I have the date in every format under the sun and also separate variable for the year,month and day seperately)

I would like a code that calculates monthly averages at certain depths.

For example to go from a matrix of [date, x, y, depth] which contain various NaNs to one which has 1:20:4000 depth in the first column repeated for every month (total of 350 months in my data set) and then corresponding monthly average for x and y.

Thank you for any help with this in advance

[John BG]

would it be possible to read a sample of the data?

Answer 1

[Mohammad Abouali]

first convert your date so that you get year and month separately. If you have the date as a string you can use datevec() command as follows:

dateVector = datevec(dateStr);
year = dateVector(:,1);
month = dateVector(:,2);

then you can use grpstats(). I suggest to create a table first, but you can also use a regular array.

dataTBL = table();
dataTBL.Year= year;
dataTBL.month= month;
dataTBL.depth = depth;
dataTBL.x = x;
dataTBL.y = y;

monthlyMean = grpstats(dataTBL, {'year',month','depth'},{@(c) (nanmean(c(:)))})

If you upload a sample data we can be of more help.

[aaron Harvey]

Thank-you, a very quick reply and it has helped me sort this out. However i now have a the probablem of multiplying by NaN in my data. How can i multiply two vectors containin NaN's such that.

a=[1 2 3 NaN 2 3]'
b=[3 2 NaN 2 1 5]'
a*b=[3 4 NaN NaN 2 15]'

[Mohammad Abouali]

I am not sure what you are asking. If you are trying to multiply two vectors element by element you need to use .* instead of * (pay attention to the dot before *).

So it would be something like this

a=[1 2 3 NaN 2 3]'
b=[3 2 NaN 2 1 5]'

a.*b
ans =
     3
     4
   NaN
   NaN
     2
    15

If one of the element is NaN, then the multiplication results would be NaN.

Since you mentinoed your data has some NaN, earlier I suggested using nanmean instead of mean.