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Jinsong Zhao

2017-Apr-30 15:17 UTC

[R] how to assign a value to a specific position of a list

Hi there,

I have a problem with assign(). Here is the demo code:

for (i in 1:10) {
    # create a list with variable name as list_1, list_2, ..., etc.
    assign(paste("list_", i, sep = ""), list())
    # I hope to assign 5 to list_?[[1]], but I don't know how to code it.
    # list_1[[1]] <- 5 # works, however
    assign(paste("list_", i, "[[1]]", sep = "", 5)
# does not work
}

How to do? Is there any alternatives? Many thanks!

Best,
Jinsong

Jinsong Zhao

2017-Apr-30 15:20 UTC

head link

[R] how to assign a value to a specific position of a list

On 2017/4/30 23:17, Jinsong Zhao wrote:> Hi there,
>
> I have a problem with assign(). Here is the demo code:
>
> for (i in 1:10) {
>    # create a list with variable name as list_1, list_2, ..., etc.
>    assign(paste("list_", i, sep = ""), list())
>    # I hope to assign 5 to list_?[[1]], but I don't know how to code
it.
>    # list_1[[1]] <- 5 # works, however
>    assign(paste("list_", i, "[[1]]", sep =
"", 5) # does not work      # wrong code in previous message, the correct on should be:
      assign(paste("list_", i, "[[1]]", sep = ""),
5) # does not work...> }
>
> How to do? Is there any alternatives? Many thanks!
>
> Best,
> Jinsong

peter dalgaard

2017-Apr-30 15:48 UTC

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[R] how to assign a value to a specific position of a list

assign(paste("list_", i, "[[1]]", sep = ""), 5)
creates a new variable with a funny name.

You'd have to parse() and eval() to make that work, something like

eval(parse(text=paste("list_",i,"[[1]]<-",5,
sep="")))

However,
-------> fortunes::fortune("parse")
If the answer is parse() you should usually rethink the question.
   -- Thomas Lumley
      R-help (February 2005)
-------

It is much easier to handle this using a data structure containing a list of
lists:

l <- rep(list(list()), 10)
for ( i in 1:10 ) 
   l[[i]][[1]] <- 5
 > On 30 Apr 2017, at 17:17 , Jinsong Zhao <jszhao at yeah.net> wrote:
> 
> Hi there,
> 
> I have a problem with assign(). Here is the demo code:
> 
> for (i in 1:10) {
>   # create a list with variable name as list_1, list_2, ..., etc.
>   assign(paste("list_", i, sep = ""), list())
>   # I hope to assign 5 to list_?[[1]], but I don't know how to code it.
>   # list_1[[1]] <- 5 # works, however
>   assign(paste("list_", i, "[[1]]", sep = "",
5) # does not work
> }
> 
> How to do? Is there any alternatives? Many thanks!
> 
> Best,
> Jinsong
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

Jeff Newmiller

2017-Apr-30 15:56 UTC

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[R] how to assign a value to a specific position of a list

My reaction is... why do you think this is a good approach to pursue?

Avoid using assign!

library( fortunes )
fortune( 236 )

If you really need another level of containment, put your multiple lists into
another list:

lst  <- lapply( 1:10, list )
lst[[1]][[1]] <- 5

-- 
Sent from my phone. Please excuse my brevity.

On April 30, 2017 8:20:17 AM PDT, Jinsong Zhao <jszhao at yeah.net>
wrote:>On 2017/4/30 23:17, Jinsong Zhao wrote:
>> Hi there,
>>
>> I have a problem with assign(). Here is the demo code:
>>
>> for (i in 1:10) {
>>    # create a list with variable name as list_1, list_2, ..., etc.
>>    assign(paste("list_", i, sep = ""), list())
>>    # I hope to assign 5 to list_?[[1]], but I don't know how to
code
>it.
>>    # list_1[[1]] <- 5 # works, however
>>    assign(paste("list_", i, "[[1]]", sep =
"", 5) # does not work
>      # wrong code in previous message, the correct on should be:
>     assign(paste("list_", i, "[[1]]", sep =
""), 5) # does not work...
>> }
>>
>> How to do? Is there any alternatives? Many thanks!
>>
>> Best,
>> Jinsong
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

Bert Gunter

2017-Apr-30 17:14 UTC

head link

[R] how to assign a value to a specific position of a list

... and moreover, note that the assignment can even be shortened to:

> for ( i in 1:10 )  l[[c(i,1)]] <- 5
?"[["  contains details, but the relevant point is:

"[[ can be applied recursively to lists, so that if the single index i
is a vector of length p, alist[[i]] is equivalent to
alist[[i1]]...[[ip]] providing all but the final indexing results in a
list."

For a less terse version, see any good online R tutorial. Lists are
extremely useful in R, and indexing is fundamental. If you haven't
spent the time to learn about these constructs, you should now before
posting further. You'll save yourself a  lot of grief and perhaps even
some embarassment.


Cheers,
Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Sun, Apr 30, 2017 at 8:48 AM, peter dalgaard <pdalgd at gmail.com>
wrote:> assign(paste("list_", i, "[[1]]", sep = ""),
5) creates a new variable with a funny name.
>
> You'd have to parse() and eval() to make that work, something like
>
> eval(parse(text=paste("list_",i,"[[1]]<-",5,
sep="")))
>
> However,
> -------
>> fortunes::fortune("parse")
>
> If the answer is parse() you should usually rethink the question.
>    -- Thomas Lumley
>       R-help (February 2005)
> -------
>
> It is much easier to handle this using a data structure containing a list
of lists:
>
> l <- rep(list(list()), 10)
> for ( i in 1:10 )
>    l[[i]][[1]] <- 5
>
>> On 30 Apr 2017, at 17:17 , Jinsong Zhao <jszhao at yeah.net>
wrote:
>>
>> Hi there,
>>
>> I have a problem with assign(). Here is the demo code:
>>
>> for (i in 1:10) {
>>   # create a list with variable name as list_1, list_2, ..., etc.
>>   assign(paste("list_", i, sep = ""), list())
>>   # I hope to assign 5 to list_?[[1]], but I don't know how to code
it.
>>   # list_1[[1]] <- 5 # works, however
>>   assign(paste("list_", i, "[[1]]", sep =
"", 5) # does not work
>> }
>>
>> How to do? Is there any alternatives? Many thanks!
>>
>> Best,
>> Jinsong
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> --
> Peter Dalgaard, Professor,
> Center for Statistics, Copenhagen Business School
> Solbjerg Plads 3, 2000 Frederiksberg, Denmark
> Phone: (+45)38153501
> Office: A 4.23
> Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

MacQueen, Don

2017-May-01 16:35 UTC

head link

[R] how to assign a value to a specific position of a list

It's not clear what you're trying to do. However, to "assign a
value to a specific position of a list", this example should show you how.

lst <- vector('list', 10)       ## see the help page for list
names(lst) <- paste0('list.',1:10)

## to assign 'a' to position 3:
pos <- 3
lst[[pos]] <- 'a'

I completely agree with Jeff Newmiller's recommendation to avoid using
assign. It's probably the wrong tool for what you're trying to do
(whatever that is).
(and note that I have borrowed Jeff's name "lst" for the list with
10 elements [not variables] whose names are "list_1"
"list_2" etc.)
(and I refuse to use "_" in R object names, but that's a personal
preference)

-Don

-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062


On 4/30/17, 8:17 AM, "R-help on behalf of Jinsong Zhao"
<r-help-bounces at r-project.org on behalf of jszhao at yeah.net> wrote:

    Hi there,
    
    I have a problem with assign(). Here is the demo code:
    
    for (i in 1:10) {
        # create a list with variable name as list_1, list_2, ..., etc.
        assign(paste("list_", i, sep = ""), list())
        # I hope to assign 5 to list_?[[1]], but I don't know how to code
it.
        # list_1[[1]] <- 5 # works, however
        assign(paste("list_", i, "[[1]]", sep =
"", 5) # does not work
    }
    
    How to do? Is there any alternatives? Many thanks!
    
    Best,
    Jinsong
    
    ______________________________________________
    R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    https://stat.ethz.ch/mailman/listinfo/r-help
    PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    and provide commented, minimal, self-contained, reproducible code.

Jinsong Zhao

2017-May-02 00:37 UTC

head link

[R] how to assign a value to a specific position of a list

Thank you very much, and your reply is helpful.

I don't like assign, and even don't use parse in my previous codes. 
However, in the case I encountered, assign and parse may be the right 
tools. Here is the code I used:

# in the workspace, there are tens directory.
# In each directory, there are lots of *.ASC file,
# with second column is the data.
# Each *.ASC file has a name with pattern i-tr-??.ASC.
# i is the directory name, tr is a group name, and ?? are the index.
# I have to collect all tr-?? into a matrix,
# and put all i-tr-?? into a list EEM_i.

for (i in dir()) {
    assign(paste("EEM_",i,sep=""), list())
    fn <- list.files(path = i, pattern = "ASC")
    tr <- sort(as.numeric(unique(unlist(lapply(strsplit(fn,
"-"),"[[",
2)))))
    for (j in 1:length(tr)) {
       fn_tr <- list.files(path = i, pattern = paste(i, tr[j],
"...ASC",
sep="-"))
       EEM_tmp <- matrix(NA,ncol = length(fn_tr),nrow = 371)
       for (k in 1:length(fn_tr)) {
          data_tmp <- read.csv(paste(i,fn_tr[k],sep="/"), header =
FALSE)
          if (dim(data_tmp)[1] != 371) next
          EEM_tmp[,k] <- data_tmp[,2]
       }
      
eval(parse(text=paste("EEM_",i,"[[",j,"]]<-","EEM_tmp",
sep="")))
    }
}

Any alternatives or improvements? Thanks a lot.

Best,
Jinsong

On 2017/4/30 23:48, peter dalgaard wrote:> assign(paste("list_", i, "[[1]]", sep = ""),
5) creates a new variable with a funny name.
>
> You'd have to parse() and eval() to make that work, something like
>
> eval(parse(text=paste("list_",i,"[[1]]<-",5,
sep="")))
>
> However,
> -------
>> fortunes::fortune("parse")
>
> If the answer is parse() you should usually rethink the question.
>    -- Thomas Lumley
>       R-help (February 2005)
> -------
>
> It is much easier to handle this using a data structure containing a list
of lists:
>
> l <- rep(list(list()), 10)
> for ( i in 1:10 )
>    l[[i]][[1]] <- 5
>
>> On 30 Apr 2017, at 17:17 , Jinsong Zhao <jszhao at yeah.net>
wrote:
>>
>> Hi there,
>>
>> I have a problem with assign(). Here is the demo code:
>>
>> for (i in 1:10) {
>>   # create a list with variable name as list_1, list_2, ..., etc.
>>   assign(paste("list_", i, sep = ""), list())
>>   # I hope to assign 5 to list_?[[1]], but I don't know how to code
it.
>>   # list_1[[1]] <- 5 # works, however
>>   assign(paste("list_", i, "[[1]]", sep =
"", 5) # does not work
>> }
>>
>> How to do? Is there any alternatives? Many thanks!
>>
>> Best,
>> Jinsong
>>

R help - May 2017 - how to assign a value to a specific position of a list

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[R] how to assign a value to a specific position of a list

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[R] how to assign a value to a specific position of a list

[R] how to assign a value to a specific position of a list

[R] how to assign a value to a specific position of a list