[R] Subsetting Data
dwinsemius at comcast.net
Thu Apr 28 21:43:17 CEST 2011
On Apr 28, 2011, at 3:38 PM, David Winsemius wrote:
> On Apr 28, 2011, at 3:13 PM, Abraham Mathew wrote:
>> I'm using the subset() function in R.
>> dat <- data.frame(one=c(6,7,8,9,10), Number=c(5,15,13,1,13))
>> subset(dat, Number >= 10)
>> However, I want to find the number of all rows who meet the
>> I've done this in the past with something like colSums or rowSums
>> or another
>> similar function.
>> But I don't remember how to get the number of elements which meet
>> function(subset(dat, Number >= 10)) #function is what i'm asking
> Daily's answer would work but if you wanted a direct answer to your
> question then try nrow or NROW:
> > nrow(subset(dat, Number >= 10))
>  3
> > NROW(subset(dat, Number >= 10))
>  3
> There is a difference and I am under the impression that NROW is
> safer in some way.
if (is.array(x) || is.data.frame(x)) nrow(x) else length(x)
So if you were doing something with tapply or a [,] subsetting
operation which might return a single dimensioned result you would
definitely want NROW.
>> In the above example, I'd run get 3 because there are 3 Number values
>> greater than 10.
> David Winsemius, MD
> West Hartford, CT
> R-help at r-project.org mailing list
> 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
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