R help - Mar 2010 - Sub-setting a data frame by partial column names?

Hi all --

I think my Python brain is missing something crucial about string
operations in R, but I cannot figure this out.

I have a large data frame with several groups of similar variables.
Similar variables are named according to their group, and I am now
writing a function to check correlations within groups.  I want to
subset the data frame by partial variable name, something along the
lines of this:

partialName <- "XXX"
subsetData <- bigData[, partialName in colnames(bigData)]

Where bigData might have 10 columns named "XXX1", "XXX2"
etc.

Many thanks for any thoughts,

Sarah

On 03/04/2010 05:51 PM, Sarah Henderson wrote:
> Hi all --
>
> I think my Python brain is missing something crucial about string
> operations in R, but I cannot figure this out.
>
> I have a large data frame with several groups of similar variables.
> Similar variables are named according to their group, and I am now
> writing a function to check correlations within groups.  I want to
> subset the data frame by partial variable name, something along the
> lines of this:
>
> partialName<- "XXX"
> subsetData<- bigData[, partialName in colnames(bigData)]
>
> Where bigData might have 10 columns named "XXX1",
"XXX2" etc.
>
Hi Sarah,

Try this:

column.names<-paste(sample(c("X","Y","Z"),100,TRUE),
  sample(c("X","Y","Z"),100,TRUE),
  sample(c("X","Y","Z"),100,TRUE),
  sample(0:9,100,TRUE),sep="")
column.names[grep("XXX",column.names,fixed=TRUE)]

Jim

Hi Jim, and thanks for your solution.  I figured one out for myself
about a minute after I posted this, and here it is if anyone else can
find it valuable:

subsetData<- bigData[,grep(partialName, colnames(bigData))]

This is smaller than your solution, but similar I think.

Cheers,

Sarah


On Thu, Mar 4, 2010 at 6:34 PM, Jim Lemon <jim at bitwrit.com.au>
wrote:
> On 03/04/2010 05:51 PM, Sarah Henderson wrote:
>>
>> Hi all --
>>
>> I think my Python brain is missing something crucial about string
>> operations in R, but I cannot figure this out.
>>
>> I have a large data frame with several groups of similar variables.
>> Similar variables are named according to their group, and I am now
>> writing a function to check correlations within groups. ?I want to
>> subset the data frame by partial variable name, something along the
>> lines of this:
>>
>> partialName<- "XXX"
>> subsetData<- bigData[, partialName in colnames(bigData)]
>>
>> Where bigData might have 10 columns named "XXX1",
"XXX2" etc.
>>
>
> Hi Sarah,
>
> Try this:
>
>
column.names<-paste(sample(c("X","Y","Z"),100,TRUE),
> ?sample(c("X","Y","Z"),100,TRUE),
> ?sample(c("X","Y","Z"),100,TRUE),
> ?sample(0:9,100,TRUE),sep="")
> column.names[grep("XXX",column.names,fixed=TRUE)]
>
> Jim
>

Sarah Henderson wrote:
> 
> 
> I think my Python brain is missing something crucial about string
> operations in R, but I cannot figure this out.
> 
> I have a large data frame with several groups of similar variables.
> Similar variables are named according to their group, and I am now
> writing a function to check correlations within groups.  I want to
> subset the data frame by partial variable name, something along the
> lines of this:
> 
With thanks to Peter Dalgaard, who sent me this 10 years ago at my first
posting. You can do it in one line though, and use <- to be a real fReak.

d = data.frame(xxx1=1:10,xx2=1:10,yy2=1:10,axx=1:10)
selcols = grep("^xx", names(d))
d[,selcols]

Dieter

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Hi Sarah,

Thanks a lot for the suggestion. It is working for me. 
subsetData<- bigData[,grep(partialName, colnames(bigData))]


But if i want to extract multiple columns along with the columns with
similar names, how do i that? Say the others column have similar values for
all the columns with similar partialnames. I tried the following

subsetData<- bigData[,grep("partialName", "Colname1",
"Colname2",
colnames(bigData))]

It did not work.
Do you have any suggestion ?

Regards,

Pankaj Barah

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