R help - Mar 2011 - Need to abstract changing name of column within loop

Hi,

I'm struggling to figure out the way to change the name of a column
from within a loop.  The problem is I can't refer to the object by its
actual variable name, since that will change each time through the
loop.  My xts object is A.
> head(A)
           A.Open A.High A.Low A.Close A.Volume A.Adjusted A.Adjusted.1
2007-01-03  34.99  35.48 34.05   34.30  2574600      34.30  11867800000
2007-01-04  34.30  34.60 33.46   34.41  2073700      34.41  11905860000
2007-01-05  34.30  34.40 34.00   34.09  2676600      34.09  11795140000
2007-01-08  33.98  34.08 33.68   33.97  1557200      33.97  11753620000
2007-01-09  34.08  34.32 33.63   34.01  1386200      34.01  11767460000
2007-01-10  34.04  34.04 33.37   33.70  2157400      33.70  11660200000

It's column names are:
> colnames(A)
[1] "A.Open"       "A.High"       "A.Low"       
"A.Close"
"A.Volume"     "A.Adjusted"   "A.Adjusted.1"

I want to change the 7th column name:
> colnames(A)[7]
[1] "A.Adjusted.1"

I need to do that through a reference to i:
> i
[1] "A"

This works:
> colnames(get(i))[7]
[1] "A.Adjusted.1"

And this is what I want to change the column name to:
> paste(i, ".MarketCap", sep = "")
[1] "A.MarketCap"

But how do I make the assignment?  This clearly doesn't work:
> colnames(get(i))[7] <-  paste(i, ".MarketCap", sep =
"")
Error in colnames(get(i))[7] <- paste(i, ".MarketCap", sep =
"") :
  could not find function "get<-"

Nor does this (it creates a new object "A.Adjusted.1" with a value of
"A.MarketCap") :

assign(colnames(get(i))[7], paste(i, ".MarketCap", sep =
""))

How can I change the name of that column within my big loop?  Any
ideas?  Thanks!

Best regards,


James

On Mar 16, 2011, at 7:58 PM, jctoll wrote:
> Hi,
>
> I'm struggling to figure out the way to change the name of a column
> from within a loop.  The problem is I can't refer to the object by its
> actual variable name, since that will change each time through the
> loop.  My xts object is A.
>
>> head(A)
>           A.Open A.High A.Low A.Close A.Volume A.Adjusted A.Adjusted.1
> 2007-01-03  34.99  35.48 34.05   34.30  2574600      34.30   
> 11867800000
> 2007-01-04  34.30  34.60 33.46   34.41  2073700      34.41   
> 11905860000
> 2007-01-05  34.30  34.40 34.00   34.09  2676600      34.09   
> 11795140000
> 2007-01-08  33.98  34.08 33.68   33.97  1557200      33.97   
> 11753620000
> 2007-01-09  34.08  34.32 33.63   34.01  1386200      34.01   
> 11767460000
> 2007-01-10  34.04  34.04 33.37   33.70  2157400      33.70   
> 11660200000
>
> It's column names are:
>> colnames(A)
> [1] "A.Open"       "A.High"       "A.Low"    
"A.Close"
> "A.Volume"     "A.Adjusted"   "A.Adjusted.1"
>
> I want to change the 7th column name:
>> colnames(A)[7]
> [1] "A.Adjusted.1"
>
> I need to do that through a reference to i:
>> i
> [1] "A"
>
It's not pretty and there may be a more direct way:
 > a
       [,1] [,2]
[1,] 1e+20 1000
[2,] 1e+02 1000
 > b <- "a"
 > assign("tmp", eval(parse(text=b)))
 > tmp
       [,1] [,2]
[1,] 1e+20 1000
[2,] 1e+02 1000
 > colnames(tmp) <- c("one","two")
 > assign( b, tmp)
 > a
        one  two
[1,] 1e+20 1000
[2,] 1e+02 1000


Trying to short circuit the process without an intermediate temporary  
structure fails:
 > colnames(eval(parse(text=b)) )<- c("two", "three")
Error in parse(`*tmp*`) : EOF whilst reading MBCS char at line 1
-- 
David
> This works:
>> colnames(get(i))[7]
> [1] "A.Adjusted.1"
>
> And this is what I want to change the column name to:
>> paste(i, ".MarketCap", sep = "")
> [1] "A.MarketCap"
>
> But how do I make the assignment?  This clearly doesn't work:
>
>> colnames(get(i))[7] <-  paste(i, ".MarketCap", sep =
"")
> Error in colnames(get(i))[7] <- paste(i, ".MarketCap", sep =
"") :
>  could not find function "get<-"
>
> Nor does this (it creates a new object "A.Adjusted.1" with a
value of
> "A.MarketCap") :
>
> assign(colnames(get(i))[7], paste(i, ".MarketCap", sep =
""))
>
> How can I change the name of that column within my big loop?  Any
> ideas?  Thanks!
>
> Best regards,
>
>
> James
>
> ______________________________________________
> 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.
David Winsemius, MD
West Hartford, CT

On Wed, Mar 16, 2011 at 6:58 PM, jctoll <jctoll at gmail.com>
wrote:
> Hi,
>
> I'm struggling to figure out the way to change the name of a column
> from within a loop. ?The problem is I can't refer to the object by its
> actual variable name, since that will change each time through the
> loop. ?My xts object is A.
>
>> head(A)
> ? ? ? ? ? A.Open A.High A.Low A.Close A.Volume A.Adjusted A.Adjusted.1
> 2007-01-03 ?34.99 ?35.48 34.05 ? 34.30 ?2574600 ? ? ?34.30 ?11867800000
> 2007-01-04 ?34.30 ?34.60 33.46 ? 34.41 ?2073700 ? ? ?34.41 ?11905860000
> 2007-01-05 ?34.30 ?34.40 34.00 ? 34.09 ?2676600 ? ? ?34.09 ?11795140000
> 2007-01-08 ?33.98 ?34.08 33.68 ? 33.97 ?1557200 ? ? ?33.97 ?11753620000
> 2007-01-09 ?34.08 ?34.32 33.63 ? 34.01 ?1386200 ? ? ?34.01 ?11767460000
> 2007-01-10 ?34.04 ?34.04 33.37 ? 33.70 ?2157400 ? ? ?33.70 ?11660200000
>
> It's column names are:
>> colnames(A)
> [1] "A.Open" ? ? ? "A.High" ? ? ? "A.Low" ? ?
? ?"A.Close"
> "A.Volume" ? ? "A.Adjusted" ? "A.Adjusted.1"
>
> I want to change the 7th column name:
>> colnames(A)[7]
> [1] "A.Adjusted.1"
>
> I need to do that through a reference to i:
>> i
> [1] "A"
>
> This works:
>> colnames(get(i))[7]
> [1] "A.Adjusted.1"
>
> And this is what I want to change the column name to:
>> paste(i, ".MarketCap", sep = "")
> [1] "A.MarketCap"
>
> But how do I make the assignment? ?This clearly doesn't work:
>
>> colnames(get(i))[7] <- ?paste(i, ".MarketCap", sep =
"")
> Error in colnames(get(i))[7] <- paste(i, ".MarketCap", sep =
"") :
> ?could not find function "get<-"
>
> Nor does this (it creates a new object "A.Adjusted.1" with a
value of
> "A.MarketCap") :
>
> assign(colnames(get(i))[7], paste(i, ".MarketCap", sep =
""))
>
> How can I change the name of that column within my big loop? ?Any
> ideas? ?Thanks!
>
I usually make a copy of the object, change it, then overwrite the original:

tmp <- get(i)
colnames(tmp)[7] <- "foo"
assign(i,tmp)

Hope that helps.
> Best regards,
>
>
> James
>
> ______________________________________________
> 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.
>
--
Joshua Ulrich  |  FOSS Trading: www.fosstrading.com