[datatable-help] Error inside [.data.table

[Andreas Borg]

Hello,

I get an error using the [-operator for a data table object that is hard 
to understand. Basically, what I want to do is the following: I have a 
data.table with a number of binary patterns, possibly including IDs or 
other additional columns. I want to process them grouped by the outcome 
of some variables, e.g. count the number of examples that have 1s in 
some specified columns. Unfortunately, I cannot reproduce the error with 
simple test data, but with data from our package RecordLinkage:

install.packages("RecordLinkage") # just for convenienve as this is not 
a common package
library(RecordLinkage)
library(data.table)
data(RLdata500)
rpairs <- compare.dedup(RLdata500, blockfld=list(5,6,7))
p <- rpairs$pairs
p[is.na(p)] <- 0
p <- data.table(p)
# Everything up to here sets up test data. Now define a key and 
aggregate by the key columns
keyCol <- c("fname_c1", "lname_c2")
key(p) <- keyCol
p[, length(fname_c2), by=keyCol]

The last expression results in:

Fehler in `[[<-.data.frame`(`*tmp*`, jj, value = 0:1) :
  replacement has 2 rows, data has 15627


However, when I construct a similar table manually, everything works fine:

expr <- quote(as.numeric(sample(0:1, 1000, replace=TRUE)))
dt <- data.table(fname_c1=eval(expr), fname_c2=eval(expr))
key(dt) <- c("fname_c1", "fname_c2")
dt[, length(fname_c2), by=c("fname_c1", "fname_c2")]

Also, with other combinations of attributes I get the first example 
working as well:

keyCol <- c("fname_c1", "lname_c2")
key(p) <- keyCol
p[, length(fname_c2), by=keyCol]


I am not even sure if the error is strictly reproducible.

Any idea what could be wrong?

Best regards,

Andreas

-- 
Andreas Borg
Medizinische Informatik

UNIVERSITÄTSMEDIZIN
der Johannes Gutenberg-Universität
Institut für Medizinische Biometrie, Epidemiologie und Informatik
Obere Zahlbacher Straße 69, 55131 Mainz
www.imbei.uni-mainz.de

Telefon +49 (0) 6131 175062
E-Mail: borg at imbei.uni-mainz.de

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