[R] Incrementing a counter in lapply
tlumley at u.washington.edu
Tue Mar 14 18:30:46 CET 2006
On Tue, 14 Mar 2006, Gabor Grothendieck wrote:
> On 3/14/06, Thomas Lumley <tlumley at u.washington.edu> wrote:
>> On Tue, 14 Mar 2006, Gabor Grothendieck wrote:
>>> On 3/14/06, Thomas Lumley <tlumley at u.washington.edu> wrote:
>>>> It is probably worth pointing out here that the R documentation does not
>>>> specify the order in which lapply() does the computation.
>>> I suspect that a huge amount of application code takes advantage
>>> of this order.
>> I don't. The order of evaluation is usually not readily observable. You
>> either have to use <<- to modify an external variable or you have to
>> produce printed or graphical output where the order matters.
>> There's probably some examples, but there are some examples of people
>> using solve(t(X) %*% W %*% X) %*% W %*% Y to compute regression
>> coefficients, too.
> By order do you mean that the result is returned in a random order
> or that the result is returned in a fixed order but computed it a random
It is returned in a fixed order, the first output corresponding to the
first input. The documentation does not specify what order it is
This in contrast to eapply(), which returns the results in a random order.
Thomas Lumley Assoc. Professor, Biostatistics
tlumley at u.washington.edu University of Washington, Seattle
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