[datatable-help] Subsetting bug?

[Gene Leynes]

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<http://stackoverflow.com/questions/13666298/why-subsetting-with-a-numeric-key-doesnt-work-with-data-table>
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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