[datatable-help] := suggestions

[Damian Betebenner]

All,

Trying to use := well but get errors and warnings and am looking for an elegant way to subset and use := together when multiple variables are being created and factors are involved.

Here's some code showing what I'm trying to do. Any help in doing this better greatly appreciated:

#########################################################
###
### Test of data.table and :=
###
#########################################################

require(data.table)


### Base data.table

test.dt <- data.table(ID=rep(1:10, 2), CONTENT_AREA=as.factor(rep(c("MATH", "READ"), each=10)), X=rnorm(10))
setkeyv(test.dt, c("ID", "CONTENT_AREA"))

test.dt


### Values to be looked up

my.lookup <- data.table(ID=1:5,  CONTENT_AREA=as.factor("MATH"))

my.lookup


### Data table to be added to the original data.table

my.additional.table <- data.table(my.lookup, VALID_CASE=factor(1, levels=1:2, labels=c("VALID_CASE", "INVALID_CASE")), Y=as.factor(letters[1:5]), Z=101:105)

my.additional.table


### First attempt with error

test.dt[my.lookup, names(my.new.table) := my.additional.table, with=FALSE, mult="first"]



### Create the variables in test.dt using := (but gives warnings and is cumbersome to have to specify the class of the variables that are going to be created)
### NOTE:


for (i in c("VALID_CASE", "Y", "Z")) {
                test.dt[, i := NA_integer_, with=FALSE, mult="first"]
                class(test.dt[[i]]) <- class(my.additional.table[[i]])
                if (is.factor(test.dt[[i]])) levels(test.dt[[i]]) <- levels(my.additional.table[[i]])
}


### Sucessfully perform the variable creation on the rows indicated by my.lookup

test.dt[my.lookup, names(my.additional.table) := my.additional.table, with=FALSE, mult="first"]



Damian Betebenner
Center for Assessment
PO Box 351
Dover, NH   03821-0351

Phone (office): (603) 516-7900
Phone (cell): (857) 234-2474
Fax: (603) 516-7910

dbetebenner at nciea.org<mailto:dbetebenner at nciea.org>
www.nciea.org<http://www.nciea.org/>



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