[R] tapply output as a dataframe

[David Winsemius]

On Feb 3, 2011, at 1:05 PM, Graves, Gregory wrote:

> Yes, as far as I can tell, "sampling.date" is a character vector of  
> the format "1/15/2008".  It resides in the leftmost column of the  
> tapply output.
>
> "station.code" are the A, B, C column headers which refer actual  
> water quality station locations, and the values below those headers  
> correspond to the "sampling.date" when samples were taken.  Actually  
> what I have done is to take the mid-point of each month and  
> calculated its mean to deal with multiple samples taken in one  
> month, and to generate NAs where no sample was taken by purposefully  
> not adding the na.rm=T to the tapply command.
>
> Normally I would do this:
>> rdate<-as.POSIXct(strptime(date,format="%m/%d/%Y")) #convert  
>> sampling.date to date R can handle
>> plot(A~rdate)
>
> If I just submit station.code like
>> A
> I get all the values for "Station A".
>
> It is in converting the sampling.date to an "rdate" that has me  
> stumped.  One reason being that in the tapply output the character  
> vector representing date has no column name.  I can't access that  
> column.

It looks like a zoo object. "zoo" objects hold their time values in  
the rownames attribute. But since its not really ordered properly, it  
may just be a table with rownames. The str() function applied to the  
object from tapply would tell you the answer.

-- 
David.

>
> Gregory A. Graves, Lead Scientist
> Everglades REstoration COoordination and VERification (RECOVER)
> Wetland Watershed Sciences / Restoration Sciences Department
> South Florida Water Management District
> Phones:  DESK: 561 / 682 - 2429
>                    CELL:  561 / 719 - 8157
>
>
> -----Original Message-----
> From: David Winsemius [mailto:dwinsemius at comcast.net]
> Sent: Thursday, February 03, 2011 12:50 PM
> To: Graves, Gregory
> Cc: r-help at r-project.org; Goodman, Patricia; Gorman, Patricia
> Subject: Re: [R] tapply output as a dataframe
>
>
> On Feb 3, 2011, at 11:29 AM, Graves, Gregory wrote:
>
>
>> My tapply output is generated as follows:
>>
>>> a=tapply(value,list(sampling.date,station.code),mean)
>
> Why not give us sampling.date (which is probably NOT really a date but
> rather a character vector) and station.code so we can show you how to
> create a more appropriate structure?
>
>>
>> which gives me this (in part):
>>
>>            A     B     C     D     E     F     G     H     I
>> J      K
>> 1/15/2008  0.004 0.027 0.019 0.015 0.035 0.022 0.007 0.038 0.042
>> 0.045 0.0350
>> 1/15/2009  0.027 0.027 0.031 0.015 0.008 0.021 0.007 0.027 0.026
>> 0.029 0.0210
>> 1/15/2010  0.016 0.020 0.015 0.022 0.015 0.013 0.007 0.014 0.019
>> 0.019 0.0180
>> 10/15/2007 0.052 0.051 0.032 0.024 0.017 0.044 0.015 0.058 0.063
>> 0.061 0.0640
>> 10/15/2008 0.042 0.054 0.030 0.017 0.024 0.030 0.019 0.044 0.047
>> 0.051 0.0390
>> 10/15/2009 0.047 0.035 0.031 0.020 0.012 0.039 0.019 0.051 0.055
>> 0.054 0.0350
>
>> The only way I can figure out how to resolve this, such that I can,
>> for example, plot station "A" against date, is to export the tapply
>> output as a csv, and then reimport.
>
>>
>> Suggestions?  I couldn't find a solution to this likely SIMPLE  
>> problem
>
> Perhaps. but we haven't really been told what the problem is, have we?
>
>> in Crawley or multiple searches of R help.
>
>>
>> Gregory A. Graves, Lead Scientist
>
>
> David Winsemius, MD
> West Hartford, CT
>
>

David Winsemius, MD
West Hartford, CT