how to get data frames within lists?

Question

I am using the following code to run simulations. How can I get a from x1? I have tried lapply below but doesn't seem to work.

library(parallel)
clusterEvalQ(cl,library(evir))
set.seed(0)
system.time(
 x1 <- parLapply(cl, 1:100000,
   function(i) {
       n1 <- rpois(1,4)
       n2<-  rpois(1,7)
       list(data.frame(a=rexp(n1, rate=0.1),a1=rexp(n1, rate=0.6)), 
            data.frame(b=rexp(n2, rate=0.7),b1=rexp(n2, rate=0.6)))

   }
  )
)

y1<-lapply(x1, '[', , "a")

Can we assume that the number of a data frame (in the case of a or a1 - 1) is known? Or should we look for this column across all data frames? — Julius Vainora
– Julius Vainora, Commented Mar 28, 2016 at 15:54
a is not a data.frame it's a vector within a data.frame. The same is true of b... You don't understand the data structures you're working with. — alexwhitworth
– alexwhitworth, Commented Mar 28, 2016 at 17:04

Julius Vainora · Accepted Answer · 2016-03-28 16:20:21Z

1

y1 <- lapply(x1, function(x) x[[1]][["a"]])

gives a required list of vector assuming that the number of a data frame is known and equals 1. More generally:

y1 <- Filter(Negate(is.null), sapply(unlist(x1, rec = FALSE), `[[`, "a"))

edited Mar 28, 2016 at 16:20

answered Mar 28, 2016 at 15:22

Julius Vainora

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1 Comment

HaagenDaz Over a year ago

thanks, i slightly changed the code above. How can I get only a or a1.

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