[datatable-help] 'by' on a numeric column produces inconsistent utput

[Arunkumar Srinivasan]

@mnel, I'm not sure I understand your output. Yours is different from the correct output, but it is also different from Kevin's. Basically, dt[, max(y), by=by] has no effect on yours and just returns back dt? 

Arun


On Thursday, December 19, 2013 at 3:50 AM, Michael Nelson wrote:

> Using
> data.table 1.8.11 (Fresh install from r-forge today)
> R version 3.0.2 (2013-09-25)
> Platform: x86_64-w64-mingw32/x64 (64-bit)
> 
> I get
> 
> by max
> 1: 0.7 0.01464054
> 2: 0.4 0.87328871
> 3: 0.4 -1.02794620
> 
> On both runs.
> 
> 
> 
> 
> ________________________________________
> From: datatable-help-bounces at lists.r-forge.r-project.org (mailto:datatable-help-bounces at lists.r-forge.r-project.org) [datatable-help-bounces at lists.r-forge.r-project.org (mailto:datatable-help-bounces at lists.r-forge.r-project.org)] on behalf of Kevin Ushey [kevinushey at gmail.com (mailto:kevinushey at gmail.com)]
> Sent: Thursday, 19 December 2013 12:54 PM
> To: datatable-help at lists.r-forge.r-project.org (mailto:datatable-help at lists.r-forge.r-project.org)
> Subject: [datatable-help] 'by' on a numeric column produces inconsistent output
> 
> I'm cross-posting this from the GitHub mirror:
> https://github.com/arunsrinivasan/datatable/issues/2
> 
> For reference, I only see this with the latest RForge version of
> data.table (1.8.11), not the CRAN version of data.table.
> 
> -----
> 
> library(data.table, lib="/Users/kevinushey/Library/R/3.1/library")
> set.seed(32)
> n <- 3
> dt <- data.table(
> y=rnorm(n),
> by=round( rnorm(n), 1)
> )
> 
> dt[,
> list(max=max(y, na.rm=TRUE)),
> by=list(by)
> ]
> 
> dt[,
> list(max=max(y, na.rm=TRUE)),
> by=list(by)
> ]
> 
> produces the output
> 
> > dt[,
> + list(max=max(y, na.rm=TRUE)),
> + by=list(by)
> + ]
> by max
> 1: 0.4 0.01464054
> 2: 0.4 0.87328871
> 3: 0.7 -1.02794620
> > 
> > dt[,
> + list(max=max(y, na.rm=TRUE)),
> + by=list(by)
> + ]
> by max
> 1: 0.4 0.8732887
> 2: 0.7 -1.0279462
> 
> For some reason, the first return is wrong, while the second (and all
> subsequent) output is correct. Any idea what's going on?
> 
> > sessionInfo()
> R Under development (unstable) (2013-12-12 r64453)
> Platform: x86_64-apple-darwin13.0.0 (64-bit)
> 
> locale:
> [1] en_CA.UTF-8/en_CA.UTF-8/en_CA.UTF-8/C/en_CA.UTF-8/en_CA.UTF-8
> 
> attached base packages:
> [1] stats graphics grDevices utils datasets methods base
> 
> other attached packages:
> [1] data.table_1.8.11 knitr_1.5 devtools_1.4.1.99
> BiocInstaller_1.13.3
> 
> loaded via a namespace (and not attached):
> [1] compiler_3.1.0 digest_0.6.4 evaluate_0.5.1 formatR_0.10
> httr_0.2 memoise_0.1
> [7] parallel_3.1.0 plyr_1.8 RCurl_1.95-4.1 reshape2_1.2.2
> stringr_0.6.2 tools_3.1.0
> [13] whisker_0.3-2
> 
> ---
> 
> Kevin
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> 


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