[datatable-help] subsetting by second key

[Arunkumar Srinivasan]

unique(Species) is of length 3, where as the 2nd entry c(1.5, 2) is of length 2.

J in J(.) is replaced with list(.) internally (using lazy evaluation), following which it’s converted to a data.table using as.data.table(list(.)).

And here your list is:

list(c("setosa", "versicolor", "virginica") , c(1.5, 2.0)) which results in the warning because it has to recycle to convert it to a data.table.

In the example you’ve linked, J(.) and CJ(.) will return the same result (because there’s just one value in 2nd column). So, the results don’t change. But the general expression is to use CJ(.) along with nomatch=0L, as you’ve done.

Those two expressions are equivalent, yes.


Arun

From: G See gsee000 at gmail.com
Reply: G See gsee000 at gmail.com
Date: June 15, 2014 at 5:45:11 PM
To: datatable-help at lists.r-forge.r-project.org datatable-help at lists.r-forge.r-project.org
Subject:  [datatable-help] subsetting by second key  

Hi,  

I want to subset a data.table using only its second key, which is  
demonstrated here  
http://stackoverflow.com/questions/15597685/subsetting-data-table-by-2nd-column-only-of-a-2-column-key-using-binary-search/15597713#15597713  

However, I need to subset with more than one value in the secondary key  

Is this warning expected? What exactly is it telling me?  

library(data.table)  
DT <- data.table(iris, key="Species,Petal.Width")  
DT[J(unique(Species), c(1.5, 2.0)), nomatch=0L]  
# Sepal.Length Sepal.Width Petal.Length Petal.Width Species  
#1: 6.0 2.2 5.0 1.5 virginica  
#2: 6.3 2.8 5.1 1.5 virginica  
#Warning message:  
#In as.data.table.list(i) :  
# Item 2 is of size 2 but maximum size is 3 (recycled leaving a  
remainder of 1 items)  


It looks like I can get what I want with either of these; can you  
confirm that both of these will always return the same result?  

DT[Petal.Width %in% c(1.5, 2.0)] # vector scan  
DT[CJ(unique(Species), c(1.5, 2.0)), nomatch=0L]  


Thanks,  
Garrett  
_______________________________________________  
datatable-help mailing list  
datatable-help at lists.r-forge.r-project.org  
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/datatable-help/attachments/20140615/7a69cb14/attachment.html>