[R] extract from a list of lists

[Greg Snow]

Terry,

I don't know if it is much cleaner or not, but you can use:

sapply(fits, `[[`, 'iter')

This calls the `[[` function (to extract list elements) on each
element of the top list, with the extra argument of `iter` to say
which element.


On Tue, Dec 27, 2022 at 10:16 AM Therneau, Terry M., Ph.D. via R-help
<r-help using r-project.org> wrote:
>
> I not uncommonly have the following paradym
>     fits <- lapply(argument, function)
>
> resulting in a list of function results.   Often, the outer call is to mclapply, and the
> function encodes some long calculation, e.g. multiple chains in an MCMC.
> Assume for illustration that each function returns a list with elements   beta, loglik,  iter.
>
> Then  sapply(fits,  function(x) x$iter)
> will give me a vector, with the number of iterations used by each instance.
>
> I've often been suspicious that there is some simple shorthand for the "grab all the
> elements named iter" that skips the explicit x$iter function.   Am I indeed overlooking
> something?    I don't expect a speed increase, just cleaner code.
>
> Terry T.
>
> --
> Terry M Therneau, PhD
> Department of Quantitative Health Sciences
> Mayo Clinic
> therneau using mayo.edu
>
> "TERR-ree THUR-noh"
>
>         [[alternative HTML version deleted]]
>
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-- 
Gregory (Greg) L. Snow Ph.D.
538280 using gmail.com