Dear all,
I encountered this strange behaviour with loops and lists. Consider this:
xl <- list()
for(i in 5:7){##loop over numeric vector
xl[[i]] <- rnorm(i)
}> xl
[[1]]
NULL
[[2]]
[1] -0.4448192 -1.3395014
[[3]]
[1] 1.3214195 -1.2968560 -0.6327795
The above lists contained a NULL element for some reason. While the code below:
xl <- list()
for(i in as.character(2:3)){##loop over character vector
xl[[i]] <- rnorm(i)
}> xl
$`2`
[1] -1.139506 2.894280
$`3`
[1] 0.0599175 1.0793515 0.4296049
This resulting list contains no extraneous elements. Is this normal? Why?
Thanks,
Liviu
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Hi,
xl<- vector("list",7)
for(i in 5:7){##loop over numeric vector
???? xl[[i]] <- rnorm(i)
?}
?xl
#[[1]]
#NULL
#
#[[2]]
#NULL
#
#[[3]]
#NULL
#
#[[4]]
#NULL
#
#[[5]]
#[1]? 0.3266762? 0.4316069? 1.2290551 -0.6725783? 1.6159861
#
#[[6]]
#[1] -2.8560618 -0.5694743 -0.7325862? 1.6786160? 0.3883842 -0.3991854
#
#[[7]]
#[1] -1.22443607? 0.66940158? 0.97476608 -0.85964961? 0.06331827 -0.40658831
#[7]? 0.24824287
xlNew<- vector("list",4)
for(i in as.character(2:3)){##loop over character vector
??? xlNew[[as.numeric(i)]] <- rnorm(i)
}
xlNew
#[[1]]
#NULL
#
#[[2]]
#[1] -2.155804? 1.780388
#
#[[3]]
#[1]? 0.4192816 -1.0142512 -0.2125988
#
#[[4]]
#NULL
A.K.
----- Original Message -----
From: Liviu Andronic <landronimirc at gmail.com>
To: "r-help at r-project.org Help" <r-help at r-project.org>
Cc:
Sent: Sunday, May 19, 2013 12:08 PM
Subject: [R] strange behaviour with loops and lists
Dear all,
I encountered this strange behaviour with loops and lists. Consider this:
xl <- list()
for(i in 5:7){##loop over numeric vector
? ? xl[[i]] <- rnorm(i)
}> xl
[[1]]
NULL
[[2]]
[1] -0.4448192 -1.3395014
[[3]]
[1]? 1.3214195 -1.2968560 -0.6327795
The above lists contained a NULL element for some reason. While the code below:
xl <- list()
for(i in as.character(2:3)){##loop over character vector
? ? xl[[i]] <- rnorm(i)
}> xl
$`2`
[1] -1.139506? 2.894280
$`3`
[1] 0.0599175 1.0793515 0.4296049
This resulting list contains no extraneous elements. Is this normal? Why?
Thanks,
Liviu
--
Do you know how to read?
http://www.alienetworks.com/srtest.cfm
http://goodies.xfce.org/projects/applications/xfce4-dict#speed-reader
Do you know how to write?
http://garbl.home.comcast.net/~garbl/stylemanual/e.htm#e-mail
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On May 19, 2013, at 18:08 , Liviu Andronic wrote:> Dear all, > I encountered this strange behaviour with loops and lists. Consider this: > xl <- list() > for(i in 5:7){##loop over numeric vector > xl[[i]] <- rnorm(i) > } >> xl > [[1]] > NULL > > [[2]] > [1] -0.4448192 -1.3395014 > > [[3]] > [1] 1.3214195 -1.2968560 -0.6327795 > > > The above lists contained a NULL element for some reason. While the code below: > xl <- list() > for(i in as.character(2:3)){##loop over character vector > xl[[i]] <- rnorm(i) > } >> xl > $`2` > [1] -1.139506 2.894280 > > $`3` > [1] 0.0599175 1.0793515 0.4296049 > > > This resulting list contains no extraneous elements. Is this normal? Why?(The first example really had 2:3, not 5:7, right?) The essential bit is that to assign to the 2nd element of a list, it needs to have at least two elements:> x <- list() > x[[2]] <- 123 > x[[1]] NULL [[2]] [1] 123 assigning to an element with a specific name just requires there is an element of that name:> x[["2"]] <- 321 > x[[1]] NULL [[2]] [1] 123 $`2` [1] 321 In both cases, x will be extended if needed, so that the required element exists. Notice that there is no relation between the name and the number of a list element; e.g., x[["2"]] is the 3rd element in the above example. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd.mes at cbs.dk Priv: PDalgd at gmail.com