[R] Extract values from multiple lists

[Dénes Tóth]

On 12/16/2014 06:06 PM, SH wrote:
> Dear List,
>
> I hope this posting is not redundant.  I have several list outputs with the
> same components.  I ran a function with three different scenarios below
> (e.g., scen1, scen2, and scen3,...,scenN).  I would like to extract the
> same components and group them as a data frame.  For example,
> pop.inf.r1 <- scen1[['pop.inf.r']]
> pop.inf.r2 <- scen2[['pop.inf.r']]
> pop.inf.r3 <- scen3[['pop.inf.r']]
> ...
> pop.inf.rN<-scenN[['pop.inf.r']]
> new.df <- data.frame(pop.inf.r1, pop.inf.r2, pop.inf.r3,...,pop.inf.rN)
>
> My final output would be 'new.df'.  Could you help me how I can do that
> efficiently?

If efficiency is of concern, do not use data.frame() but create a list 
and add the required attributes with data.table::setattr (the setattr 
function of the data.table package). (You can also consider creating a 
data.table instead of a data.frame.)

# some largish lists
a1 <- list(x = rnorm(1e6), y = rnorm(1e6))
a2 <- list(x = rnorm(1e6), y = rnorm(1e6))
a3 <- list(x = rnorm(1e6), y = rnorm(1e6))

# amount of memory allocated
gc(reset=TRUE)

# get names of the objects
out_names <- ls(pattern="a[[:digit:]]$")

# create a list
out <- lapply(lapply(out_names, get), "[[", "x")

# note that no copying occured
gc()

# decorate the list
data.table::setattr(out, "names", out_names)
data.table::setattr(out, "row.names", seq_along(out[[1]]))
class(out) <- "data.frame"

# still no copy
gc()

# output
head(out)


HTH,
   Denes


>
> Thanks in advance,
>
> Steve
>
> P.S.:  Below are some examples of summary outputs.
>
>
>> summary(scen1)
>                  Length Class  Mode
> aql                1   -none- numeric
> rql                1   -none- numeric
> alpha              1   -none- numeric
> beta               1   -none- numeric
> n.sim              1   -none- numeric
> N                  1   -none- numeric
> n.sample           1   -none- numeric
> n.acc              1   -none- numeric
> lot.inf.r          1   -none- numeric
> pop.inf.n       2000   -none- list
> pop.inf.r       2000   -none- list
> pop.decision.t1 2000   -none- list
> pop.decision.t2 2000   -none- list
> sp.inf.n        2000   -none- list
> sp.inf.r        2000   -none- list
> sp.decision     2000   -none- list
>> summary(scen2)
>                  Length Class  Mode
> aql                1   -none- numeric
> rql                1   -none- numeric
> alpha              1   -none- numeric
> beta               1   -none- numeric
> n.sim              1   -none- numeric
> N                  1   -none- numeric
> n.sample           1   -none- numeric
> n.acc              1   -none- numeric
> lot.inf.r          1   -none- numeric
> pop.inf.n       2000   -none- list
> pop.inf.r       2000   -none- list
> pop.decision.t1 2000   -none- list
> pop.decision.t2 2000   -none- list
> sp.inf.n        2000   -none- list
> sp.inf.r        2000   -none- list
> sp.decision     2000   -none- list
>> summary(scen3)
>                  Length Class  Mode
> aql                1   -none- numeric
> rql                1   -none- numeric
> alpha              1   -none- numeric
> beta               1   -none- numeric
> n.sim              1   -none- numeric
> N                  1   -none- numeric
> n.sample           1   -none- numeric
> n.acc              1   -none- numeric
> lot.inf.r          1   -none- numeric
> pop.inf.n       2000   -none- list
> pop.inf.r       2000   -none- list
> pop.decision.t1 2000   -none- list
> pop.decision.t2 2000   -none- list
> sp.inf.n        2000   -none- list
> sp.inf.r        2000   -none- list
> sp.decision     2000   -none- list
>
> 	[[alternative HTML version deleted]]
>
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