[datatable-help] best way of eval-ing a list of quoted expressions

[Frank Erickson]

Hi,

I'm wondering what the most idiomatic or efficient approach is...? Here's
my example:

expr_nonlin = list(
  early = quote(tt/TT*(tt/TT < .2)),
  late  = quote(tt/TT*(tt/TT > .8))
)

# eval on a single expr works
data.table(tt=1,TT=100)[,early:=eval(expr_nonlin$early)][]

# lapply eval does not work
data.table(tt=1,TT=100)[,names(expr_nonlin):=lapply(expr_nonlin,eval)][]

# (1) envir fixes it
DT <- data.table(tt=1,TT=100)
DT[,names(expr_nonlin):=lapply(expr_nonlin,eval,envir=DT)][]

# (2) or a for loop
DT <- data.table(tt=1,TT=100)
for (i in names(expr_nonlin)) DT[,(i):=eval(expr_nonlin[[i]])]

(1) and (2) both work. Is either preferable?

(1) calls [.data.table fewer times, but messes around with environments,
which always seem fragile.

------------------

One more quick question: In approach (1), is there a way to skip the
names(zzz):= part? I see that this doesn't work:

DT <- data.table(tt=1,TT=100)
DT[,do.call(`:=`,lapply(expr_nonlin,eval,envir=DT))][]


Thanks,

Frank
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/datatable-help/attachments/20150114/035b1682/attachment.html>