[R] Reading dates in R using SQL and otherwise (and some interesting behavior by the data editor)

[Paul Miller]

Hello Everyone,
 
I am a newbie with about a month's worth of experience using R. I've just spent 
a little time learning how to work with date values. Mostly, this has involved 
converting text values into dates.
 
So far, I've managed to figure out how to do this in R proper using as.Date. 
However, I'm still struggling with doing this using SQL and RODBC.
 
In the process of learning to create date values in R proper, I noticed some 
interesting behavior on the part of the data editor. At first, this led me to 
believe that my efforts had been unsuccessful. The output from my R console 
below illustrates this behavior.
 
> test <- mydata
> test$test_date <- as.Date(test$ae_datestarted, format='%m/%d/%Y')
> class(test$test_date)
[1] "Date"
> mode(test$test_date)
[1] "numeric"
> 
> fix(test)
 
(At this point, I clicked on the test_date column)

Warning: class discarded from column ‘test_date’
> 
> class(test$test_date)
[1] "character"
> mode(test$test_date)
[1] "character"
> 
 
When I run my code, it works correctly. But when I open the data frame in the 
data editor and click on the test_date column, the editor says that it is 
character. And beyond that, the editor discards the class for test_date. Should 
the editor do this? Or is it my fault for trying to look at test_date in the 
editor in the first place? In SAS, I'm used to creating data and then opening 
the dataset to look at what I've done. Maybe I shouldn't be doing this in R 
though.
 
Returning to the issue of converting text values to dates using SQL (Server) 
and RODBC. Does anyone know how ot do this? I've been trying to do this using 
things like Cast and Convert. Usually, these attempts fail. When SQL Server 
does seem to be sending something back, it appears that R cannot accept it. Any 
help with this problem would be greatly appreciated.
 
Thanks,
 
Paul     
 


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