Message-ID: <1360706916.81040.YahooMailNeo@web142604.mail.bf1.yahoo.com>
Date: 2013-02-12T22:08:36Z
From: arun
Subject: grabbing from elements of a list without a loop
In-Reply-To: <CAN2xGJbjv0tYWtqTsxjGJLLU-pmFwKm3QR2z0CtkTr6WHRkkiQ@mail.gmail.com>
Hi,
?mapply(`[`,mylist,list(1,2,0),SIMPLIFY=FALSE)
#[[1]]
#? a
#1 1
#2 2
#[[2]]
?# b
#1 5
#2 6
#[[3]]
#data frame with 0 columns and 2 rows
A.K.
----- Original Message -----
From: Dimitri Liakhovitski <dimitri.liakhovitski at gmail.com>
To: r-help <r-help at r-project.org>
Cc:
Sent: Tuesday, February 12, 2013 4:33 PM
Subject: [R] grabbing from elements of a list without a loop
Hello!
# I have a list with several data frames:
mylist<-list(data.frame(a=1:2,b=2:3),
? ? ? ? ? data.frame(a=3:4,b=5:6),data.frame(a=7:8,b=9:10))
(mylist)
# I want to grab only one specific column from each list element
neededcolumns<-c(1,2,0)? # number of the column I need from each element of
the list
# Below, I am doing it using a loop:
newlist<-NULL
for(i in 1:length(mylist) ) {
? newlist[[i]]<-mylist[[i]] [neededcolumns[i]]
}
newlist<-do.call(cbind,newlist)
(newlist)
I was wondering if there is any way to avoid the loop above and make it
faster.
In reality, I have a much longer list, each of my data frames is much
larger and I have to do it MANY-MANY times.
Thanks a lot!
Dimitri Liakhovitski
gfk.com <http://marketfusionanalytics.com/>
??? [[alternative HTML version deleted]]
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