R help - Aug 2011 - Getting data from an *.RData file into a data.frame object.

Hi, all.

I'm new to R.  I've been a SAS programmer for 20 years.

I seem to be having trouble with the most basic task - bringing a table in
an *.RData file into a data.frame object.

Here's how I created the *.RData file.

library(RODBC)
db <- odbcConnect("*******")
df <- sqlQuery(
    db
  , "select * from schema.table where year(someDate)=2006"
)
save(
    df
  , file="C:/Documents and Settings/userName/My
Documents/table2006.RData"
)
dim(df)
remove(df)
odbcClose(db)
remove(db)
detach("package:RODBC")

Next, I moved that data file (table2006.RData) to another workstation - not
at the client site.

Now, I need to get that data file into a data.frame object.  I know this
should be simple, but I can't seem to find out how to do that.  I tried the
following.  First, after opening R without doing anything, RGui used 35,008
KB of memory.  I submitted the following.
> debt2006 <- load("T:/R.Data/table2006.RData")
Memory used by RGui jumped to 191,512 KB.  So, it looks like the data
loaded.  However, debt2005 is of type character instead of data.frame.
> ls()
[1] "debt2005"
> class(debt2005)
[1] "character"
>
Help, please.

Ed

Ed Heaton
Project Manager, Sr. SAS Developer
Data and Analytic Solutions, Inc.
10318 Yearling Drive
Rockville, MD 20850
Office: 301-520-7414
eheaton at dasconsultants.com
www.dasconsultants.com <http://www.dasconsultants.com/> 
CMMI ML-2, SBA 8(a) & SDB, WBE (WBENC), MBE (VA & MD)

ed at heaton.name

(Re: http://www.r-project.org/posting-guide.html)

On 12/08/2011 3:12 PM, Ed Heaton wrote:
> Hi, all.
>
> I'm new to R.  I've been a SAS programmer for 20 years.
>
> I seem to be having trouble with the most basic task - bringing a table in
> an *.RData file into a data.frame object.
>
> Here's how I created the *.RData file.
>
> library(RODBC)
> db<- odbcConnect("*******")
> df<- sqlQuery(
>      db
>    , "select * from schema.table where year(someDate)=2006"
> )
> save(
>      df
>    , file="C:/Documents and Settings/userName/My
Documents/table2006.RData"
> )
> dim(df)
> remove(df)
> odbcClose(db)
> remove(db)
> detach("package:RODBC")
>
> Next, I moved that data file (table2006.RData) to another workstation - not
> at the client site.
>
> Now, I need to get that data file into a data.frame object.  I know this
> should be simple, but I can't seem to find out how to do that.  I tried
the
> following.  First, after opening R without doing anything, RGui used 35,008
> KB of memory.  I submitted the following.
>
> >  debt2006<- load("T:/R.Data/table2006.RData")
>
> Memory used by RGui jumped to 191,512 KB.  So, it looks like the data
> loaded.  However, debt2005 is of type character instead of data.frame.
>
> >  ls()
> [1] "debt2005"
> >  class(debt2005)
> [1] "character"
> >
>
> Help, please.
save() and load() work with multiple objects, and the objects keep their 
names.  So your object would be recreated as "df" after the load.

If you just want to save the data from one object without its name, use 
saveRDS() and readRDS().

Duncan Murdoch

On Aug 12, 2011, at 21:12 , Ed Heaton wrote:
> Hi, all.
> 
> I'm new to R.  I've been a SAS programmer for 20 years.
> 
> I seem to be having trouble with the most basic task - bringing a table in
> an *.RData file into a data.frame object.
> 
> Here's how I created the *.RData file.
> 
> library(RODBC)
> db <- odbcConnect("*******")
> df <- sqlQuery(
>    db
>  , "select * from schema.table where year(someDate)=2006"
> )
> save(
>    df
>  , file="C:/Documents and Settings/userName/My
Documents/table2006.RData"
> )
> dim(df)
> remove(df)
> odbcClose(db)
> remove(db)
> detach("package:RODBC")
> 
> Next, I moved that data file (table2006.RData) to another workstation - not
> at the client site.
> 
> Now, I need to get that data file into a data.frame object.  I know this
> should be simple, but I can't seem to find out how to do that.  I tried
the
> following.  First, after opening R without doing anything, RGui used 35,008
> KB of memory.  I submitted the following.
> 
>> debt2006 <- load("T:/R.Data/table2006.RData")
> 
> Memory used by RGui jumped to 191,512 KB.  So, it looks like the data
> loaded.  However, debt2005 is of type character instead of data.frame.
> 
>> ls()
> [1] "debt2005"
>> class(debt2005)
> [1] "character"
>> 
> 
> Help, please.
> 
The load/save mechanism handles multiple objects. You can't really assign
the result of load(), its return value is just a vector of object names
("df", right?).

So look in your workspace for an object called "df". Then assign it to
debt2005. AFAIK, this won't duplicate quite as much as it sounds it might.

For a single-step variation, try something like

debt2005 <- local({load(myfile); df})

> Ed
> 
> Ed Heaton
> Project Manager, Sr. SAS Developer
> Data and Analytic Solutions, Inc.
> 10318 Yearling Drive
> Rockville, MD 20850
> Office: 301-520-7414
> eheaton at dasconsultants.com
> www.dasconsultants.com <http://www.dasconsultants.com/> 
> CMMI ML-2, SBA 8(a) & SDB, WBE (WBENC), MBE (VA & MD)
> 
> ed at heaton.name
> 
> (Re: http://www.r-project.org/posting-guide.html)
> 
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
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