R help - Aug 2006 - unquoting

I would like a function to strip quotes off character strings. I should 
work like this:

 > A <- matrix(1:6, nrow = 2, ncol=3)
 > AF <- as.data.frame(A)
 > names(AF) <- c("First","Second","Third")
 > AF
   First Second Third
1     1      3     5
2     2      4     6
 > names(AF)[2]
[1] "Second"
 > attach(AF)
 > unquote(names(AF)[2])
[1] 3 4

Of course what I actually get is

Error: couldn't find function "unquote"

The reason that I want to do this is that I have a frame with a rather 
large number of variables and I would like to loop over the names and 
print out various descriptive summaries of the variable's distribution.

OK, OK, I could just go

 > AF[,2]
[1] 3 4

but once I thought of unquoting I have some sort of inner need to know 
how to do it!

Cheers,

Murray
-- 
Dr Murray Jorgensen      http://www.stats.waikato.ac.nz/Staff/maj.html
Department of Statistics, University of Waikato, Hamilton, New Zealand
Email: maj at waikato.ac.nz                                Fax 7 838 4155
Phone  +64 7 838 4773 wk    Home +64 7 825 0441    Mobile 021 1395 862

Try these

   get(names(AF)[2])
   AF["Second"] # this one different than the rest
   AF[["Second"]]
   AF[, "Second"]
   AF$Second


On 8/20/06, Murray Jorgensen <maj at waikato.ac.nz>
wrote:
> I would like a function to strip quotes off character strings. I should
> work like this:
>
>  > A <- matrix(1:6, nrow = 2, ncol=3)
>  > AF <- as.data.frame(A)
>  > names(AF) <-
c("First","Second","Third")
>  > AF
>   First Second Third
> 1     1      3     5
> 2     2      4     6
>  > names(AF)[2]
> [1] "Second"
>  > attach(AF)
>  > unquote(names(AF)[2])
> [1] 3 4
>
> Of course what I actually get is
>
> Error: couldn't find function "unquote"
>
> The reason that I want to do this is that I have a frame with a rather
> large number of variables and I would like to loop over the names and
> print out various descriptive summaries of the variable's distribution.
>
> OK, OK, I could just go
>
>  > AF[,2]
> [1] 3 4
>
> but once I thought of unquoting I have some sort of inner need to know
> how to do it!
Try:

sapply(names(AF), function(nm) mean(AF[nm]))

# same as previous but names a bit nicer

sapply(names(AF), function(nm) mean(AF[nm]), USE.NAMES = FALSE)

sapply(AF, mean)

colMeans(AF)
>
> Cheers,
>
> Murray
> --
> Dr Murray Jorgensen      http://www.stats.waikato.ac.nz/Staff/maj.html
> Department of Statistics, University of Waikato, Hamilton, New Zealand
> Email: maj at waikato.ac.nz                                Fax 7 838 4155
> Phone  +64 7 838 4773 wk    Home +64 7 825 0441    Mobile 021 1395 862
>
> ______________________________________________
> 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.
>

Murray Jorgensen <maj at waikato.ac.nz> writes:
> I would like a function to strip quotes off character strings. I should 
> work like this:
> 
>  > A <- matrix(1:6, nrow = 2, ncol=3)
>  > AF <- as.data.frame(A)
>  > names(AF) <-
c("First","Second","Third")
>  > AF
>    First Second Third
> 1     1      3     5
> 2     2      4     6
>  > names(AF)[2]
> [1] "Second"
>  > attach(AF)
>  > unquote(names(AF)[2])
> [1] 3 4
> 
> Of course what I actually get is
> 
> Error: couldn't find function "unquote"
> 
> The reason that I want to do this is that I have a frame with a rather 
> large number of variables and I would like to loop over the names and 
> print out various descriptive summaries of the variable's distribution.
> 
> OK, OK, I could just go
> 
>  > AF[,2]
> [1] 3 4
> 
> but once I thought of unquoting I have some sort of inner need to know 
> how to do it!
Anything wrong with

AF[,names(AF)[2]]

or

AF[[names(AF)[2]]]

or for that matter

eval(as.name(names(AF)[2]), envir=AF)

??

-- 
   O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

?get

I really think this has nothing to do with `quoting', rather to do with 
evaluating variables from their names. At first I though you were looking 
for noquote(), which does unquote in the conventional sense.
> noquote(names(AF)[2])
[1] Second
> get(names(AF)[2])
[1] 3 4

On Sun, 20 Aug 2006, Murray Jorgensen wrote:
> I would like a function to strip quotes off character strings. I should 
> work like this:
> 
>  > A <- matrix(1:6, nrow = 2, ncol=3)
>  > AF <- as.data.frame(A)
>  > names(AF) <-
c("First","Second","Third")
>  > AF
>    First Second Third
> 1     1      3     5
> 2     2      4     6
>  > names(AF)[2]
> [1] "Second"
>  > attach(AF)
>  > unquote(names(AF)[2])
> [1] 3 4
> 
> Of course what I actually get is
> 
> Error: couldn't find function "unquote"
> 
> The reason that I want to do this is that I have a frame with a rather 
> large number of variables and I would like to loop over the names and 
> print out various descriptive summaries of the variable's distribution.
> 
> OK, OK, I could just go
> 
>  > AF[,2]
> [1] 3 4
> 
> but once I thought of unquoting I have some sort of inner need to know 
> how to do it!
> 
> Cheers,
> 
> Murray
> 
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595