R help - Aug 2007 - how do i use the get function to obtain an element from a list...

my problem can be explained with the following example:

x <- 1:12
y <- 13:24
a <- data.frame(x = x, y = y)

## if i write
a$x
## it returns
[1]  1  2  3  4  5  6  7  8  9 10 11 12

## but the function get doesn't recognize a$x. Instead it produces the
following error:
get("a$x")
Error in get(x, envir, mode, inherits) : variable "a$x" was not found

i intend to do it inside a loop, using a new object (and hence, a new
name) for each iteration (i.e., instead of a$x, it would be a$1, a$2,
a$3, and so on, for a million times).

i would greatly appreciate it if someone could help me on this issue,

thanks in advance,

Juan Manuel Barreneche,
Zoolog?a de Vertebrados,
Facultad de Ciencias,
UDELAR, Uruguay.

eval(parse(text=("a$x"). You can only use get when it's an object.
a$x isn't.


-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch [mailto:r-help-bounces at
stat.math.ethz.ch] On Behalf Of Juan Manuel Barreneche
Sent: Tuesday, August 21, 2007 3:35 PM
To: r-help at stat.math.ethz.ch
Subject: [R] how do i use the get function to obtain an element from alist...

my problem can be explained with the following example:

x <- 1:12
y <- 13:24
a <- data.frame(x = x, y = y)

## if i write
a$x
## it returns
[1]  1  2  3  4  5  6  7  8  9 10 11 12

## but the function get doesn't recognize a$x. Instead it produces the
following error:
get("a$x")
Error in get(x, envir, mode, inherits) : variable "a$x" was not found

i intend to do it inside a loop, using a new object (and hence, a new
name) for each iteration (i.e., instead of a$x, it would be a$1, a$2, a$3, and
so on, for a million times).

i would greatly appreciate it if someone could help me on this issue,

thanks in advance,

Juan Manuel Barreneche,
Zoolog?a de Vertebrados,
Facultad de Ciencias,
UDELAR, Uruguay.

______________________________________________
R-help at stat.math.ethz.ch 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.
--------------------------------------------------------

This is not an offer (or solicitation of an offer) to buy/se...{{dropped}}

On 8/21/2007 3:35 PM, Juan Manuel Barreneche wrote:
> my problem can be explained with the following example:
> 
> x <- 1:12
> y <- 13:24
> a <- data.frame(x = x, y = y)
> 
> ## if i write
> a$x
> ## it returns
> [1]  1  2  3  4  5  6  7  8  9 10 11 12
> 
> ## but the function get doesn't recognize a$x. Instead it produces the
> following error:
> get("a$x")
> Error in get(x, envir, mode, inherits) : variable "a$x" was not
found
a$x is an expression, which you could evaluate, not a variable, which 
you could get.
> 
> i intend to do it inside a loop, using a new object (and hence, a new
> name) for each iteration (i.e., instead of a$x, it would be a$1, a$2,
> a$3, and so on, for a million times).
> 
> i would greatly appreciate it if someone could help me on this issue,
Why name things?  I'd use something like

for (i in 1:1000000) print(a[[i]])

Duncan Murdoch

Hi, you can try this:

eval(parse(text="a$x"))

-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

On 21/08/07, Juan Manuel Barreneche <jumanbar@gmail.com>
wrote:
>
> my problem can be explained with the following example:
>
> x <- 1:12
> y <- 13:24
> a <- data.frame(x = x, y = y)
>
> ## if i write
> a$x
> ## it returns
> [1]  1  2  3  4  5  6  7  8  9 10 11 12
>
> ## but the function get doesn't recognize a$x. Instead it produces the
> following error:
> get("a$x")
> Error in get(x, envir, mode, inherits) : variable "a$x" was not
found
>
> i intend to do it inside a loop, using a new object (and hence, a new
> name) for each iteration (i.e., instead of a$x, it would be a$1, a$2,
> a$3, and so on, for a million times).
>
> i would greatly appreciate it if someone could help me on this issue,
>
> thanks in advance,
>
> Juan Manuel Barreneche,
> Zoología de Vertebrados,
> Facultad de Ciencias,
> UDELAR, Uruguay.
>
> ______________________________________________
> R-help@stat.math.ethz.ch 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]]

One simple way that I haven't seen mentioned yet is to do:

 > get("a")$x

(which of course allows further variants such as get("a")$x[3:6] ...)


-- Tony Plate

Juan Manuel Barreneche wrote:
> my problem can be explained with the following example:
> 
> x <- 1:12
> y <- 13:24
> a <- data.frame(x = x, y = y)
> 
> ## if i write
> a$x
> ## it returns
> [1]  1  2  3  4  5  6  7  8  9 10 11 12
> 
> ## but the function get doesn't recognize a$x. Instead it produces the
> following error:
> get("a$x")
> Error in get(x, envir, mode, inherits) : variable "a$x" was not
found
> 
> i intend to do it inside a loop, using a new object (and hence, a new
> name) for each iteration (i.e., instead of a$x, it would be a$1, a$2,
> a$3, and so on, for a million times).
> 
> i would greatly appreciate it if someone could help me on this issue,
> 
> thanks in advance,
> 
> Juan Manuel Barreneche,
> Zoolog?a de Vertebrados,
> Facultad de Ciencias,
> UDELAR, Uruguay.
> 
> ______________________________________________
> R-help at stat.math.ethz.ch 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.
>