R help - Nov 2001 - of c, cat, paste, and lists??

Still trying to get a handle on c, cat, paste, and lists.

Here is my current problem.  I have a good number of vectors that I 
want to selectively combine into a dataframe.  The exact name of the 
vectors changes in a looping arrangement but can easily be grepped. The 
problem is: how can I use a list produced by a grep in a data.frame command: 
i.e.
> ls()
 [1] "a"            "a1"           "a2"          
"a3"           "b3"
 [6] "c"            "compet1"      "compet10"    
"compet2"      "compet3"
[11] "compet4"      "compet5"      "compet6"     
"compet7"      "compet8"
[16] "compet9"      "d"            "g"           
"h"
"last.warning"
[21] "listing"      "pop1"         "pop10"       
"pop2"         "pop3"
[26] "pop4"         "pop5"         "pop6"        
"pop7"         "pop8"
[31] "pop9"         "s"            "vote1"       
"vote10"       "vote2"
[36] "vote3"        "vote4"        "vote5"       
"vote6"        "vote7"
[41] "vote8"        "vote9"        "X"

Now I want the "vote?" variables in a dataframe.  I can grep them
by
> grep("vote",ls(),value=T)
 [1] "vote1"  "vote10" "vote2"  "vote3" 
"vote4"  "vote5"  "vote6"  "vote7"
 [9] "vote8"  "vote9"

seems like some sort of:
mydata _ data.frame(as.list(grep("vote",ls(),value=T)))

should work, but doesn't.   The the list isn't being fed into the
data.frame
function properly, but I can't figure out how it needs to be feed.

Any help greatly appreciated.


========================================Curt Taylor
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On Thu, 29 Nov 2001, Michaell Taylor wrote:
>
> Now I want the "vote?" variables in a dataframe.  I can grep them
by
> > grep("vote",ls(),value=T)
>  [1] "vote1"  "vote10" "vote2" 
"vote3"  "vote4"  "vote5"  "vote6" 
"vote7"
>  [9] "vote8"  "vote9"
>
> seems like some sort of:
> mydata _ data.frame(as.list(grep("vote",ls(),value=T)))
>
> should work, but doesn't.   The the list isn't being fed into the
data.frame
> function properly, but I can't figure out how it needs to be feed.
>
There are two problems here.

The first is that you want the list of 10 names to be 10 arguments to
data.frame, not one argument as you have here. The second problem is that
you need to convert them from strings to variable names.

If  nm<-grep("vote",ls(),value=T)
then the second problem is fixed by using as.name() on the string to turn
them into names
	lapply(nm,as.name)
The first problem is fixed with the do.call() function, which takes a
single list and turns its elements into arguments for a function
	do.call("data.frame", lapply(nm, as.name))

So for example
R> b<-1:10
R> c<-1:10
R> d<-1:10
R> 
do.call("data.frame",lapply(c("b","c","d"),as.name))
    b  c  d
1   1  1  1
2   2  2  2
3   3  3  3
4   4  4  4
5   5  5  5
6   6  6  6
7   7  7  7
8   8  8  8
9   9  9  9
10 10 10 10


	-thomas

Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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