R help - Jul 2008 - with lapply() how can you retrieve the name of the object

In the following code, I'd like to be able to create a new variable
containing the value of the names of the list.


a <- data.frame(var.1 = 1:5)
b <- data.frame(var.1 = 11:15)

test.list <- list(a=a, b=b)

# in this case, names(test.list) is "a" and "b"

# and I'd like to use lapply() so that
# I get something that looks like
# var.1 var.2
#     1  a
#     2  a
#     3  a
#etc.

new.list <- lapply(test.list, function(x) {x$var.2 <- names(x)
                                            x} )


# the above clearly doesn't do it.  How do you pull out the names of the
thing that is being lapplied?

Thanks,
Andrew

	[[alternative HTML version deleted]]

Dear Andrew,

It's not the best solution but it does what you need:

a <- data.frame(var.1 = 1:5)
b <- data.frame(var.1 = 11:15)
test.list <- list(a=a, b=b)
res=do.call(rbind,test.list)
res$var.2=substr(rownames(res),1,1)
rownames(res)=NULL
res


HTH,

Jorge


On Fri, Jul 18, 2008 at 6:21 PM, Andrew Yee <yee@post.harvard.edu> wrote:
> In the following code, I'd like to be able to create a new variable
> containing the value of the names of the list.
>
>
> a <- data.frame(var.1 = 1:5)
> b <- data.frame(var.1 = 11:15)
>
> test.list <- list(a=a, b=b)
>
> # in this case, names(test.list) is "a" and "b"
>
> # and I'd like to use lapply() so that
> # I get something that looks like
> # var.1 var.2
> #     1  a
> #     2  a
> #     3  a
> #etc.
>
> new.list <- lapply(test.list, function(x) {x$var.2 <- names(x)
>                                            x} )
>
>
> # the above clearly doesn't do it.  How do you pull out the names of
the
> thing that is being lapplied?
>
> Thanks,
> Andrew
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> 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.
>
	[[alternative HTML version deleted]]

forgot one step:
> z <- lapply(names(test.list), function(x){
+     cbind(test.list[[x]], var.2=x)
+ })
> names(z) <- names(test.list)
> z
$a
  var.1 var.2
1     1     a
2     2     a
3     3     a
4     4     a
5     5     a

$b
  var.1 var.2
1    11     b
2    12     b
3    13     b
4    14     b
5    15     b
>

On Fri, Jul 18, 2008 at 6:21 PM, Andrew Yee <yee at post.harvard.edu>
wrote:
> In the following code, I'd like to be able to create a new variable
> containing the value of the names of the list.
>
>
> a <- data.frame(var.1 = 1:5)
> b <- data.frame(var.1 = 11:15)
>
> test.list <- list(a=a, b=b)
>
> # in this case, names(test.list) is "a" and "b"
>
> # and I'd like to use lapply() so that
> # I get something that looks like
> # var.1 var.2
> #     1  a
> #     2  a
> #     3  a
> #etc.
>
> new.list <- lapply(test.list, function(x) {x$var.2 <- names(x)
>                                            x} )
>
>
> # the above clearly doesn't do it.  How do you pull out the names of
the
> thing that is being lapplied?
>
> Thanks,
> Andrew
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

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