[R] Need to aggregate large dataset by week...

[danielrev]

Hi all, 

I have a large dataset with ~8600 observations that I want to compress to
weekly means. There are 9 variables (columns), and I have already added a
"week" column with 51 weeks. I have been looking at the functions:
aggregate, tapply, apply, etc. and I am just not savvy enough with R to
figure this out on my own, though I'm sure it's fairly easy. I also have the
Dates (month/day/year) for all of the observations, but I figured just
having a week column may be easier. If someone wanted to show me how to
organize this data using a date function and aggregating by month that would
be useful too!  

Here's an example of the data set, with only 5 of the variables and 10 of
8600 obs.:

     week    rainfall windspeed   winddir      temp   oakdepth
1       1  0.20000000   0.89000  245.9200  1.150000   4.400000
2       1  0.00000000   0.84000  292.8800  1.190000   5.300000
3       1  0.20000000   0.74000  258.5400  1.360000   6.000000
4       1  0.00000000   0.93000    3.7000  1.430000   4.400000
5       1  0.20000000   0.69000   37.8200  1.560000   5.200000
6       1  0.00000000   0.80000   17.2900  1.690000   4.400000
7       1  0.20000000   0.70000   28.7300  1.880000   5.000000
8       1  0.20000000   1.12000  294.3700  1.930000   6.000000
9       1  0.00000000   1.21000  274.9700  1.800000   4.400000
10      1  0.00000000   1.31000  279.2400  1.860000   5.800000

...so after about 170 observations it changes to week 2, and so on.

I've tried something like this, but its only one variable's mean, and I
would rather have the rows=weeks and columns= the different variables. 

< tapply(metdata$rainfall,metdata$week,FUN=mean)
          1           2           3           4           5           6 
0.080952381 0.101190476 0.379761905 0.179761905 0.000000000 0.295238095 
          7           8           9          10          11          12 
0.146428571 0.015476190 0.163888889 0.098809524 0.065476190 0.215476190 

Hope this is enough information and that I'm not just re-asking an old
question. Thanks so much in advance for any help. 



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