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choosing multiple columns

7 messages · John Kane, Ista Zahn, Sachinthaka Abeywardana +2 more

John Kane
# 
mydata[ , 1:8]


Or let's say you only one the 4th, 6th and 8th columns

mydata[ , c(4,6,8)]

and so on.  

There are several good intro's available on the R website that will walk you through this type of thing.

If you're a recovering SAS or SPSS user this paper may be of real help www.et.bs.ehu.es/~etptupaf/pub/R/RforSAS&SPSSusers.pdf


John Kane
Kingston ON Canada
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Ista Zahn
# 
Hi Sachin,

There are at least two ways. The safer way is to use a regular
expression to find the matching columns, like this:

a <- initial_data[grep("^OFB[0-9]+", names(initial_data))]

Alternatively, if you know that the columns you want are the first 8
you can select them by position, like this:

a <- initial_data[1:8]

Best,
Ista

On Sat, Aug 11, 2012 at 7:59 AM, Sachinthaka Abeywardana
<sachin.abeywardana at gmail.com> wrote:
Ista Zahn
# 
On Sat, Aug 11, 2012 at 8:51 AM, Sachinthaka Abeywardana
<sachin.abeywardana at gmail.com> wrote:
Right, so use my first method. This does not depend on the position of
the columns.

Best,
Ista
arun
# 
HI,

Try this:

dat1<-as.data.frame(matrix(rnorm(50,5),ncol=10))
colnames(dat1)<-paste0("OFB",1:10)
#to select first 8 columns - easy method

dat1[,1:8]
#2nd method
wanted<-paste0("OFB",1:8)
dat1[,colnames(dat1)%in%wanted]

#3rd method
#regular expression to select 3rd, 5th columns
dat1[grep("[[:alnum:]][c(3,5)]",colnames(dat1))]

#???? OFB3???? OFB5
#1 6.378474 7.490392
#2 5.323282 4.728561
#3 5.415081 4.661548
#4 4.000541 5.286831
#5 3.598919 6.080370


dat2<-data.frame(dat1,CFB=rnorm(5,15))
#select columns having OFB as column name

dat2[grep("OFB",colnames(dat2))]
#select 4-8 columns

dat2[grep("[4-8]",colnames(dat2))]

?# ?? OFB4???? OFB5???? OFB6???? OFB7???? OFB8
#1 4.545049 7.490392 5.441275 3.433050 4.656184
#2 5.015531 4.728561 5.429073 5.268677 5.569176
#3 5.533485 4.661548 5.586189 4.694112 5.209213
#4 6.427448 5.286831 5.521572 4.036457 5.532234
#5 5.500054 6.080370 6.259925 3.946102 4.554102

Hope this helps.

A.K.







----- Original Message -----
From: Sachinthaka Abeywardana <sachin.abeywardana at gmail.com>
To: r-help at r-project.org
Cc: 
Sent: Saturday, August 11, 2012 7:59 AM
Subject: [R] choosing multiple columns

Hi all,

I have a data frame that has the columns OFB1, OFB2, OFB3,... OFB10.

How do I select the first 8 columns efficiently without typing each and
every one of them. i.e. I want something like:

a<-data.frame(initial_data$OFB1-10) #i know this is wrong, what would be
the correct syntax?

Thanks,
Sachin

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1 day later
David Winsemius
#
On Aug 11, 2012, at 6:01 AM, Ista Zahn wrote:

            

      
      
      
    

        
I would counsel greater consideration of the possible ranges of the  
column names. Even using a variation on Ista Zahn's method intended to  
deliver on the first 8 will fail if the range of possible values is  
greater than 10 in number or the numbers do not start from 1.

If the numbers of the columns do start from 1, you could try this

grep("^OFB[1-8]", paste0("OFB", 1:100) , value=TRUE )[1:8]

Otherwise  consider these efforts;

 > set.seed(123); test <- sample( paste0("OFB", 1:100), 20)
 > sort(test)[1:8]
[1] "OFB21" "OFB27" "OFB29" "OFB4"  "OFB41" "OFB42" "OFB5"  "OFB50

 > grep("^OFB[1-8]", test , value=TRUE )[1:8]
[1] "OFB29" "OFB79" "OFB41" "OFB86" "OFB5"  "OFB50" "OFB83" "OFB51"


Note that even this does not get what you want which is =

 > test[order(as.numeric( sub("OFB", "", test)))][1:8]
[1] "OFB4"  "OFB5"  "OFB9"  "OFB21" "OFB27" "OFB29" "OFB41" "OFB42"

There is also a function named mixedsort in Greg Warnes package gtools  
which automatically splits the alpha and numeric components of of an  
alphanumeric vector and then orders by the two of them separately.

Something like this might achieve:

 > test[ order( sub("[0-9]+","", test),   # an alpha sort .. followed  
by numeric sort
                as.numeric(gsub("[[:alpha:]]*([[:digit:]]*)", '\\1',  
test) ) )]

  [1] "OFB4"  "OFB5"  "OFB9"  "OFB21" "OFB27" "OFB29" "OFB41" "OFB42"  
"OFB50" "OFB51" "OFB60" "OFB77" "OFB78"
[14] "OFB79" "OFB83" "OFB86" "OFB87" "OFB91" "OFB94" "OFB98"


gtools::ixedsort is based on gtools::mixedorder and has more  
sophistication, for instance the attempt to identify spaces and  
delimiters.