You are chasing ghosts of performance past, Denes. The data.frame
function causes no problems, and if it is used then the OP would not need
to presume they know the internal structure of the data frame.
See below. (I am using R3.1.2.)
a1 <- list(x = rnorm(1e6), y = rnorm(1e6))
a2 <- list(x = rnorm(1e6), y = rnorm(1e6))
a3 <- list(x = rnorm(1e6), y = rnorm(1e6))
# get names of the objects
out_names <- ls(pattern="a[[:digit:]]$")
# amount of memory allocated
gc(reset=TRUE)
# Explicitly call data frame
out2 <- data.frame( a1=a1[["x"]], a2=a2[["x"]], a3=a3[["x"]] )
# No copying.
gc()
# Your suggested retreival method
out3a <- lapply( lapply( out_names, get ), "[[", "x" )
names( out3a ) <- out_names
# The "obvious" way to finish the job works fine.
out3 <- do.call( data.frame, out3a )
# No copying... well, you do end up with a new list in out3, but the data
itself doesn't get copied.
gc()
On Tue, 16 Dec 2014, D?nes T?th wrote:
On 12/16/2014 06:06 PM, SH wrote:
Dear List,
I hope this posting is not redundant. I have several list outputs with the
same components. I ran a function with three different scenarios below
(e.g., scen1, scen2, and scen3,...,scenN). I would like to extract the
same components and group them as a data frame. For example,
pop.inf.r1 <- scen1[['pop.inf.r']]
pop.inf.r2 <- scen2[['pop.inf.r']]
pop.inf.r3 <- scen3[['pop.inf.r']]
...
pop.inf.rN<-scenN[['pop.inf.r']]
new.df <- data.frame(pop.inf.r1, pop.inf.r2, pop.inf.r3,...,pop.inf.rN)
My final output would be 'new.df'. Could you help me how I can do that
efficiently?
If efficiency is of concern, do not use data.frame() but create a list and
add the required attributes with data.table::setattr (the setattr function of
the data.table package). (You can also consider creating a data.table instead
of a data.frame.)
# some largish lists
a1 <- list(x = rnorm(1e6), y = rnorm(1e6))
a2 <- list(x = rnorm(1e6), y = rnorm(1e6))
a3 <- list(x = rnorm(1e6), y = rnorm(1e6))
# amount of memory allocated
gc(reset=TRUE)
# get names of the objects
out_names <- ls(pattern="a[[:digit:]]$")
# 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
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