[R] Subsetting Data

[David Winsemius]

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  
>> Number>=10
>> condition.
>>
>> 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  
>> that
>> condition.
>>
>> function(subset(dat, Number >= 10))   #function is what i'm asking  
>> about
>
> 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))
> [1] 3
>
> > NROW(subset(dat, Number >= 10))
> [1] 3
>
> There is a difference and I am under the impression that NROW is  
> safer in some way.

 > NROW
function (x)
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
>
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David Winsemius, MD
West Hartford, CT