[R] Working With Variables Having Different Lengths

[David Winsemius]

On Oct 21, 2011, at 1:04 PM, Rich Shepard wrote:

> On Fri, 21 Oct 2011, Weidong Gu wrote:
>
>> No easy way out with missing data problems, all imputations are  
>> based on
>> some strong and untestable assumptions.
>
>  Thanks for the insights.
>
>  Let me rephrase my question in a way that should work: is there a  
> way to
> subset my comprehensive data frame ('chemdata') to select only those  
> rows
> that have values for two different parameters (i.e., in the same  
> column)?

The last part ("in the same column") does not make sense, since I was  
interpreting the term "parameter" to mean a value in a particular  
column. Assuming these are R NA's then logical indexing:

with( chemdata, chemdata[!is.na(param1) & !is.na(param2) , ])

If you are talking about extracting different text features from a  
single character field then look at `grepl`.

patt1 <- "S2"  # any appearance of that string
patt2 <- "E5"  # any appearance of that string
with( chemdata, chemdata[ grepl(patt1, param1) & grepl(patt2,  
param1) , ])

>
>  I suspect not. But, I can select from the database table on those  
> criteria
> and read in a new R data frame.

That to should b possible. Specifics are sorely lacking at this point,  
however.

>
> Rich
>
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David Winsemius, MD
West Hartford, CT