> -----Original Message-----
> From: r-help-boun...@r-project.org
> [mailto:r-help-boun...@r-project.org] On Behalf Of Gabor Grothendieck
> Sent: Thursday, December 31, 2009 3:15 PM
> To: donahc...@me.com
> Cc: r-help@r-project.org
> Subject: Re: [R] iterating over a data frame the R way?
>
> This iterates functions f over successive rows of mytable:
>
> apply(mytable, 1, f)
Unless all columns of the data.frame mytable are numeric
apply() is not usually a good way to go, as it converts the
data.frame to a matrix, coercing all the columns to a common
type, often character. E.g.,
> mytable <- data.frame(
start_time=seq(as.POSIXct("2009-12-31 15:27"), by="hours", len=12),
end_time=seq(as.POSIXct("2009-12-31 15:27"), by="days", len=12))
> apply(mytable, 1, function(row)row['end_time']-row['start_time'])
Error in row["end_time"] - row["start_time"] :
non-numeric argument to binary operator
Try apply(mytable,1,class) to see that all rows are character
data.
I prefer columnwise operations like the following when they
are feasible. They directly express what you want to do
and are quick to execute.
> mytable$duration <- mytable$end_time - mytable$start_time
> mytable
start_time end_time duration
1 2009-12-31 15:27:00 2009-12-31 15:27:00 0 secs
2 2009-12-31 16:27:00 2010-01-01 15:27:00 82800 secs
...
11 2010-01-01 01:27:00 2010-01-10 15:27:00 828000 secs
12 2010-01-01 02:27:00 2010-01-11 15:27:00 910800 secs
The expression
> mytable <- within(mytable, duration <- end_time - start_time)
is syntactic sugar for the one I gave above.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
>
> or if you want to use SQL on R data frames then see sqldf
> http://sqldf.googlecode.com
>
> On Thu, Dec 31, 2009 at 5:52 PM, <donahc...@me.com> wrote:
> > In this specific case I'm going to do another select, from
> a different table
> > with the where clause being based on the start_time and end_time.
> >
> > select * from table_name where time >= start_time and time
> <= end_time;
> >
> >
> > On Dec 31, 2009, at 3:57 PM, John Kane wrote:
> >
> >> Uh what do you want to do to it/them?
> >>
> >> Here are a couple of R-type commands on a data.frame.
> >>
> >> mydata <- data.frame(vec1 = seq(19,109, by=10),
> >> vec2 =seq(30,120, by=10))
> >>
> >> mydata[,1]+mydata[,2]
> >> apply(mydata, 2, mean)
> >>
> >>
> >>
> >> --- On Thu, 12/31/09, donahc...@me.com <donahc...@me.com> wrote:
> >>
> >>> From: donahc...@me.com <donahc...@me.com>
> >>> Subject: [R] iterating over a data frame the R way?
> >>> To: r-help@r-project.org
> >>> Received: Thursday, December 31, 2009, 2:44 PM
> >>> Hi,
> >>>
> >>> I have a data frame that was create by issuing a select
> >>> against my sqlite database. I want to get each row
> >>> from the data frame and use the each of the column
> >>> values. The data frame looks like this:
> >>>
> >>> start_time end_time
> >>> 09:30:00 10:00:00
> >>> 10:00:01 10:30:00
> >>> etc
> >>>
> >>> Can a point me to a tutorial/example of doing this? I
> >>> the other programming languages I'm familiar with I would
> >>> just loop over the frame and access the elements, but I
> >>> believe that's not the R way and can't find examples of
> >>> doing this.
> >>>
> >>> Thanks!
> >>>
> >>> ______________________________________________
> >>> R-help@r-project.org
> >>> mailing list
> >>> https://stat.ethz.ch/mailman/listinfo/r-help
> >>> PLEASE do read the posting guide
> >>> http://www.R-project.org/posting-guide.html
> >>> and provide commented, minimal, self-contained,
> >>> reproducible code.
> >>>
> >>
> >>
> >>
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> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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