[datatable-help] Subsetting bug?

[jim holtman]

this sounds like FAQ 7.31


> x <- seq(0,1,.1)

> print(x,digits = 20)
 [1] 0.00000000000000000000 0.10000000000000000555
0.20000000000000001110 0.30000000000000004441
 [5] 0.40000000000000002220 0.50000000000000000000
0.60000000000000008882 0.70000000000000006661
 [9] 0.80000000000000004441 0.90000000000000002220 1.00000000000000000000

try using:

 quantile = seq(0,100,10)

and then test for integer values



On Fri, Jan 11, 2013 at 10:10 AM, Gene Leynes <gleynes+r at gmail.com> wrote:
>
> Yesterday I was having a problem subsetting based on a numeric key.  I had
> some quantile data and I could get the 10% and 20%, but getting the 30%
> failed.  I was using quantile==.1, quantile==.2, etc.
>
> Thanks to the FAQ I realize that I should be using J to subset and setting
> the key first,
> Thanks to StackOverflow I realize now that I should using J to subset on
> numeric keys fixes the problem.
>
> However, this doesn't explain why using a vector search would sometimes work
> and sometimes fail.
>
> Thank you,
>    Gene Leynes
>
>
>>
>> library(data.table)
> data.table 1.8.6  For help type: help("data.table")
>>
>> set.seed(1)
>>
>> ## Make an example data table
>> dat = data.table(
> + index = 1:1e5,
> + groups = sample(letters[1:3], 1e5, replace=TRUE),
> + values = rnorm(1e5))
>>
>> ## Calculate some quantiles for each group
>> dat_quants = dat[
> +         i=TRUE,
> +         j=list(
> +             quantile = seq(0,1,.1),
> +             value = quantile(values, seq(0,1,.1))),
> +         keyby=groups]
>>
>> ## Print the 10% 20% and 30% quantiles... but 30% doesn't work
>> dat_quants[quantile==.1, ]
>    groups quantile     value
> 1:      a      0.1 -1.284277
> 2:      b      0.1 -1.280095
> 3:      c      0.1 -1.291173
>> dat_quants[quantile==.2, ]
>    groups quantile      value
> 1:      a      0.2 -0.8413631
> 2:      b      0.2 -0.8397591
> 3:      c      0.2 -0.8423560
>> dat_quants[quantile==.3, ]
> Empty data.table (0 rows) of 3 cols: groups,quantile,value
>>
>>
>> ## Changing to character will allow all of them to work
>> dat_quants$quantile = as.character(dat_quants$quantile)
>>
>
>> sessionInfo()
> R version 2.15.2 (2012-10-26)
> Platform: x86_64-w64-mingw32/x64 (64-bit)
>
> locale:
> [1] LC_COLLATE=English_United States.1252
> [2] LC_CTYPE=English_United States.1252
> [3] LC_MONETARY=English_United States.1252
> [4] LC_NUMERIC=C
> [5] LC_TIME=English_United States.1252
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] data.table_1.8.6 geneorama_1.0
>>
>>
>
>
>
>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.