[R] Avoiding Loops When Iterating Over Statement That Updates Its Input

Alan Lue alan.lue at gmail.com
Wed May 26 08:52:18 CEST 2010

Come to think of it, we can't save the output of each invocation and
concatenate it later, since we need the output as input for the next


On Tue, May 25, 2010 at 11:43 PM, Alan Lue <alan.lue at gmail.com> wrote:
> Since `for' loops are slow in R, and since `apply' functions are
> faster, I was wondering whether there were a way to use an apply
> function—or to otherwise avoid using a loop—when iterating over a
> statement that updates its input.
> For example, here's some such code:
> r.seq <- 2 * (1 / d$Dt[1] - 1)
> for (i in 2:nrow(d)) {
>  rf <- uniroot(bdt.deviation, interval=c(0, 1), D.T=d$Dt[i], r.prior=r.seq)
>  r.seq <- append(r.seq, rf$root)
> }
> The call to `uniroot()' both updates `r.seq' and reads it as input.
> We could save the output of each invocation of `uniroot()' and
> concatenate it later, but is there a better way to write this (i.e.,
> to execute more quickly) while updating `r.seq' in each iteration?
> Alan

Alan Lue
Master of Financial Engineering
UCLA Anderson School of Management

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