[R] Descriptive Stats from Data Frame

[David Winsemius]

On Aug 30, 2011, at 5:00 PM, Rich Shepard wrote:

>  I don't find how to do what I need to do in Dalgaard or 'R  
> Cookbook', so
> I'm asking here.
>
>  I have a data frame with water chemistry data and I want to start
> exploring these data. There are three factors (site, date, chemical)
> associated with each measurement. The data frame looks like this:
>
>> summary(chemdata)
>                             site_id.sample_date.param.quant

It appears that your original file was delimited by "|" and your used  
something else, perhaps the default white-space setting? I think you  
need to go back and do your input operations again with sep="|"

(Or you could provide str() on the data.frame rather than making us  
guess.)
-- 
David

> BC-0.5|1996-04-19|Arsenic|0.01              :    1
> BC-0.5|1996-04-19|Calcium|76.56             :    1
> BC-0.5|1996-04-19|Chloride|12               :    1
> BC-0.5|1996-04-19|Magnesium|43.23           :    1
> BC-0.5|1996-04-19|Sulfate|175               :    1
> BC-0.5|1996-04-19|Total Dissolved Solids|460:    1
> (Other)                                     :14880
>
>  I want first to calculate (and plot) descriptive stats by chemical,
> ignoring site and date and telling R to ignore missing data.  
> (Incorporating
> those factors will occur later.) What I have not been able to figure  
> out is
> how to specify the command to, for example, calculate mean and sd for
> Arsenic. My floundering and thrashing includes attempts like these:
>
>> mean(chemdata.param="Arsenic")
> Error in is.numeric(x) : 'x' is missing
>> mean(chemdata.quant, param="Arsenic")
> Error in mean(chemdata.quant, param = "Arsenic") :
>  object 'chemdata.quant' not found
>> mean(chemdata$quant, param="Arsenic")
> [1] NA
> Warning message:
> In mean.default(chemdata$quant, param = "Arsenic") :
>  argument is not numeric or logical: returning NA
>
>  As a newcomer to R I've done a lot of reading, yet all the examples  
> use
> nicely structured data to illustrate the point being made. I need to  
> work
> with my data and learn how to specify columns and write correct  
> commands for
> the analyses I need. Please point me in the right direction.
>
> Rich
>
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David Winsemius, MD
West Hartford, CT