R help - Jul 2009 - quoting expressions in a list

Dear R-help,

I am having quite a difficult time coming up with what I want to do involving
named lists.

I have a list of logical expressions, and I would really like it if the
"names" of the components of the list were identical to the
corresponding logical expression.

So, as an example: 

df.example <- data.frame(a = 1:10, b = rnorm(10, 5))

list.example <- list(df.example$a > 7,
                     df.example$b < 4)

Now what I'd really like is to name the components, and get the results of
the following line without having to specify the right-hand side individually
for each component:

names(list.example) <- c("df.example$a > 7", "df.example$b
< 4")


Any ideas?  

Best Regards,
Erik Iverson

Try this:
> s <- c("df.example$a > 7", "df.example$b < 4")
> sapply(s, function(x) eval(parse(text = x)))
      df.example$a > 7 df.example$b < 4
 [1,]            FALSE             TRUE
 [2,]            FALSE             TRUE
 [3,]            FALSE            FALSE
 [4,]            FALSE            FALSE
 [5,]            FALSE            FALSE
 [6,]            FALSE            FALSE
 [7,]            FALSE             TRUE
 [8,]             TRUE            FALSE
 [9,]             TRUE            FALSE
[10,]             TRUE             TRUE


On Thu, Jul 16, 2009 at 4:44 PM, Erik Iverson<eiverson at nmdp.org>
wrote:
> Dear R-help,
>
> I am having quite a difficult time coming up with what I want to do
involving named lists.
>
> I have a list of logical expressions, and I would really like it if the
"names" of the components of the list were identical to the
corresponding logical expression.
>
> So, as an example:
>
> df.example <- data.frame(a = 1:10, b = rnorm(10, 5))
>
> list.example <- list(df.example$a > 7,
> ? ? ? ? ? ? ? ? ? ? df.example$b < 4)
>
> Now what I'd really like is to name the components, and get the results
of the following line without having to specify the right-hand side individually
for each component:
>
> names(list.example) <- c("df.example$a > 7",
"df.example$b < 4")
>
>
> Any ideas?
>
> Best Regards,
> Erik Iverson
>
> ______________________________________________
> 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.
>

On Thu, Jul 16, 2009 at 4:44 PM, Erik Iverson<eiverson at nmdp.org>
wrote:
> I have a list of logical expressions, and I would really like it if the
"names" of the components of the list were identical to the
corresponding logical expression.
>
> So, as an example:
>
> df.example <- data.frame(a = 1:10, b = rnorm(10, 5))
>
> list.example <- list(df.example$a > 7,
> ? ? ? ? ? ? ? ? ? ? df.example$b < 4)
>
> Now what I'd really like is to name the components, and get the results
of the following line without having to specify the right-hand side individually
for each component:
>
> names(list.example) <- c("df.example$a > 7",
"df.example$b < 4")
Something like this, perhaps?:
> listx <- function(...)
structure(list(...),names=tail(as.list(substitute(c(...))),-1))
> list.example <- list(df.example$a > 7, df.example$b < 4)
> listx(df.example$a > 7, df.example$b < 4)
$`df.example$a > 7`
 [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE  TRUE

$`df.example$b < 4`
 [1]  TRUE FALSE FALSE FALSE FALSE  TRUE FALSE  TRUE FALSE FALSE