On Aug 11, 2012, at 6:01 AM, Ista Zahn wrote:
On Sat, Aug 11, 2012 at 8:51 AM, Sachinthaka Abeywardana
<sachin.abeyward...@gmail.com> wrote:
I should have mentioned that I do not know the number index of the
columns,
but regardless, thanks for the responses
Right, so use my first method. This does not depend on the position of
the columns.
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.
--
David.
Best,
Ista
On Sat, Aug 11, 2012 at 10:46 PM, Ista Zahn <istaz...@gmail.com>
wrote:
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.abeyward...@gmail.com> wrote:
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
David Winsemius, MD
Alameda, CA, USA
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