[R] how do I read only specific columns using read.csv or other read function

[Juliet Hannah]

I was not able to follow the solution posted. Could you demonstrate
this technique on an example
data set. Thanks!

dat <- data.frame(a = letters[1:3], b = LETTERS[1:3], c = 1:3, d = 3:1)

On Wed, Jul 2, 2008 at 1:13 PM, Charles C. Berry <cberry at tajo.ucsd.edu> wrote:
> On Wed, 2 Jul 2008, Ben Tupper wrote:
>
>>
>> On Jul 2, 2008, at 6:53 AM, Philip James Smith wrote:
>>
>>> Hi R people:
>>>
>>> I have huge files with as many as 5000 columns. I'd really like to read
>>> only certain columns of those files. I know column names I want to read.
>>>
>>> I looked at the documentation of read.csv . Although there is a col.names
>>> option, it allows users to specify the names of the columns, rather than to
>>> pick the columns of interest.
>>>
>>> Any suggestions on how to pick the columns I want to read only, rather
>>> than the entire file, would be greatly appreciated.
>
>
> There is a unix utility called 'cut' that enables stuff like
>
>   columns.1.3.5.to.7 <- read.csv( pipe( "cut -d, -f1,3,5-7 your.file" ) )
>
> and using
>
>        col.pos <- match(names.of.variables.you.want,
>                         scan("your.file", what=character(0), nlines=1 )
>
> will enable you to set up the call to pipe.
>
> HTH,
>
> Chuck
>
>>>
>>
>> Hello,
>>
>> I think you want explicitly set the colClasses argument such that the
>> columns you *don't* want are set to NULL and all others are set to
>> appropriate classes.
>>
>> Cheers,
>> Ben
>>
>>
>>
>>
>>
>>
>>> Phil Smith
>>> Duluth, GA
>>>
>>> ______________________________________________
>>> 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.
>>
>> Ben Tupper
>> PemaquidRiver at tidewater.net
>>
>> I GoodSearch for Ashwood Waldorf School.
>>
>> Raise money for your favorite charity or school just by searching the
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>>
>> ______________________________________________
>> 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.
>>
>
> Charles C. Berry                            (858) 534-2098
>                                            Dept of Family/Preventive
> Medicine
> E mailto:cberry at tajo.ucsd.edu               UC San Diego
> http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901
>
> ______________________________________________
> 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.
>