[R] Applying a function to categorized data?

[R. Michael Weylandt]

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Michael


On Thu, Apr 12, 2012 at 2:52 PM, steven mosher <moshersteven at gmail.com> wrote:
>  Welcome to R and the list.
>
>  Others may suggest books ( Nutshell was my first ) but first there are
> some things that will help you
>  both in programming and getting help on the list.
>
>  You should post executable code in your question. So, build a toy example
> of the data.frame you have
> and show what you tried. Folks here should be able to run your toy example
> and  show you how to get the answer you want.
>
> For your problem I'm guessing that aggregate() would be one path
>
> ?aggregate
>
>  you will need to specify   "by"  to aggregate by month
>
> Steve
>
> On Thu, Apr 12, 2012 at 7:10 AM, Robert Latest <boblatest at gmail.com> wrote:
>
>> Hi all,
>>
>> I'm just getting started in R. My problem is the following:
>>
>> I have a data frame (v1) with lots of production data measurements.
>> Each row contains a single measurement ('ARI_MIT') with a timestamp. I
>> want to "lump" the data by months with their mean and standard
>> deviation.
>>
>> I have already successfully managed to do the lumping by adding
>> another column to my data frame:
>>
>> v1$MONTH = strftime(v1$TIMESTAMP, "%y%m")
>>
>> This makes a nice month-wise boxplot of my data, although I don't have
>> an idea why:
>> boxplot(v1$ARI_MIT ~ v1$MONTH)
>>
>> I don't need this plotted, though, but in the form of a new data frame
>> with three columns: the month, the mean, and the standard deviation of
>> all values from that month.
>>
>> I tried un-stacking v1 into a list of vectors and then looping over
>> its elements, calculating the mean of each group:
>>
>> for (i in unstack(v1, v1$ARI_MIT ~ v1$MONTH)) { write(mean(i), "") }
>>
>> This works, but how do I get the data into a data frame? With the
>> month labels in a column? They are not avaliable inside the loop body.
>>
>> I know I need to get a book on R.
>>
>> Thanks,
>> robert
>>
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
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> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.