[R] Strange result from single [] extract operator

[William Dunlap]

> First, I tried
>  library(datasets)
> > data<-airquality
> > data[nrow(data)-1:nrow(data),]
> 
> and received 152 rows sorted desc. Could you explain why it worked this way? I changed
> the extract line to:
> data[(nrow(data)-1):nrow(data),]
> 
> and then I received what I wanted but still am curious about the performance of my
> previous code.

Back up a little and compare
    nrow(data)-1:nrow(data)
to
    (nrow(data)-1):nrow(data)
or compare
   3-1:3
to
   (3-1):3

Then look at the help file for "Syntax".

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of rafael.7 at poczta.fm
> Sent: Saturday, September 28, 2013 8:18 AM
> To: r-help at r-project.org
> Subject: [R] Strange result from single [] extract operator
> 
> Hi All,
> 
> I am using Rx64 3.0.1 on Windows 7 x64, and wanted to get two last rows from dataset.
> First, I tried
>  library(datasets)
> > data<-airquality
> > data[nrow(data)-1:nrow(data),]
> 
> and received 152 rows sorted desc. Could you explain why it worked this way? I changed
> the extract line to:
> data[(nrow(data)-1):nrow(data),]
> 
> and then I received what I wanted but still am curious about the performance of my
> previous code.
> 
> Yours faithfully,
> Rafał
> 
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