## regriding an irregular matrix

on 7 May 2013

### Andrei Bobrov (view profile)

Dear all,

I have a 3D irregular matrix in time and position below :

A = 3000 x 3

Column1 = time (vary from 2002-2005)

Column2 = Longitude (vary from 40-50)

Column3 = Value

A = [2Jan2002 40 65

`   6Jan2002 45 22`
`   8Jan2002 43 45`
`   8Jan2002 49 64`
`   30Jan2002 42 78`
`   4Feb2001 43 56`
`   6Feb2001 47 67`
`       :     :  :`
`   23Nov2005 44 76`
`   3Dec2005 42 89`
`   5Dec2005 48 67`
`   9Dec2005 44 78`
`   13Dec2005 41 89`
`   19Dec2005 49 34`
`   23Dec2005 45 67`
`   24Dec2005 43 88  `
`   31Dec2005 47 34];`

I want to regridding this irregular data in time and position into regular matrix based on monthly (2002-2005; so 48 month) and 1 degree lon position (40-50; so 10 points), in summary the output mtrix will be 10x48.

Some points longitude will have NaN value cause no record in this months at x longitude.

Anyone can help?

Best regards,

Cedric Wannaz

### Cedric Wannaz (view profile)

on 7 May 2013

This is not a valid array as it mixes strings and numeric values. How are your data truly stored at this point? If you have time, longitude, and value, you just need a 2D array, as you are mentioning later in the question when you define the dimension of your final array. Do you have in fact something like a 3 columns CSV or Excel file with the original data? If so, assuming that we can treat "31Dec2005"-like timestamps correctly, how do you want to summarize values on a per month basis; is it a simple average?

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### Andrei Bobrov (view profile)

on 8 May 2013
Edited by Andrei Bobrov

### Andrei Bobrov (view profile)

on 10 May 2013

If you have data as text file - yourdata.txt (eg):

```   2Jan2002 40 65
6Jan2002 45 22
8Jan2002 43 45
8Jan2002 49 64
30Jan2002 42 78
4Feb2002 43 56
6Feb2002 47 67
23Nov2005 44 76
3Dec2005 42 89
5Dec2005 48 67
9Dec2005 44 78
13Dec2005 41 89
19Dec2005 49 34
23Dec2005 45 67
24Dec2005 43 88
31Dec2005 47 34```

```f=fopen('yourdata.txt');
c = textscan(f,'%s %f %f');
fclose(f);
[y,m] = datevec(c{1});
[m1,y1] = ndgrid(1:12,2002:2005);
[i2,i2] = ismember([y,m],[y1(:),m1(:)],'rows');
[j2,j2] = ismember(round(c{2}),40:50);
out = accumarray([i2,j2],c{3},[48,10],@mean,nan); % [EDITED]
```

m0xty Wilopo

### m0xty Wilopo (view profile)

on 11 May 2013

This is work! Thanks Andrei

### m0xty Wilopo (view profile)

on 8 May 2013

Yes, the date is datenum precisely, I just want to show that the first column is date in string. It is in numeric.

### Cedric Wannaz (view profile)

on 8 May 2013
Edited by Cedric Wannaz

### Cedric Wannaz (view profile)

on 8 May 2013

A general approach could be the following, assuming that you have this matrix A with datenums in the first row.

` [y, m] = datevec(A(:,1)) ;`
``` dateId = ((y - min(y))*12 + m).' ;
nYears = range(y) + 1 ;```
``` lonId  = A(:,2) - min(A(:,2)) + 1 ;
nLon   = range(A(:,2)) + 1 ;                 % You might want to fix this
% instead of having it flexible.
dataArray = nan(nLon, nYears*12) ;
ind = sub2ind(size(dataArray), lonId, dateId) ;
dataArray(ind) = A(:,3) ;```

Now, as mentioned in my comment, we should improve it a bit if you can have cases where there are multiple values for the same pairs dateId/lonId. Just let me know and we can extend it using ACCUMARRAY.

### m0xty Wilopo (view profile)

on 9 May 2013

Dear Cedric and Andrei :)...Many THANKS! As usual it was really helpful. However if I have data at same longitude, I want to averaging it (mean) how to do that ie:

```   2Jan2002 40 65
6Jan2002 45 22    ---> So I will have value 24 instead of 48
7Jan2002 45 26
8Jan2002 43 45
8Jan2002 43.1 51 ---> result will be 48 at lon 43
8Jan2002 49 64
30Jan2002 42 78
4Feb2002 43 56
6Feb2002 47 67
23Nov2005 44 76
3Dec2005 42 89
5Dec2005 48 67
9Dec2005 44 78
13Dec2005 41 89
19Dec2005 49 34
23Dec2005 45 67
24Dec2005 43 88
31Dec2005 47 34```

How to do that? Andrei giving answer using accumarray in my previous question but it was for another data set in same longitude. But now I want averaging it at multi longitude/position.

Andrei Bobrov

### Andrei Bobrov (view profile)

on 10 May 2013

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