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

Paul Gilbert pgilbert at bank-banque-canada.ca
Thu Apr 8 23:38:24 CEST 2010

I can use as.Date() on the result from an sql date field, but this may depend on the backend database engine too. There may also be some sensitivity to character set encoding used on the database and the client, and from you email it looks a bit like you could have some problems in this respect.

Paul Gilbert

>-----Original Message-----
>From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
>On Behalf Of Paul Miller
>Sent: April 8, 2010 11:14 AM
>To: r-help at r-project.org
>Subject: [R] Reading dates in R using SQL and otherwise (and
>someinteresting behavior by the data editor)
>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
>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.
>Paul    Â
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La version française suit le texte anglais.


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