[R] Making cuts on multivariate data

[David Winsemius]

On Aug 29, 2010, at 10:50 PM, Erik Ramberg wrote:

> I'm a newbie to R and  I was hoping someone could answer a simple  
> question.  I want to read in an ASCII file with 3 columns - x,y,z.   
> Let's say there is a lot of data - 100,000 entries.  I then want to  
> histogram x values that pass arbitrary (and complicated) cuts on y  
> and/or z.  Likewise, I want to make a scatterplot with x and y, with  
> a cut on z values.  Perhaps you have to redefine the vectors first.
>
> I'm thinking along the lines of
> hist(x) for y>0 .and. sqrt(z)<4

If the data is in a dataframe named dta with columns x,y, and z then:

with( dta[which( dta$y > 0 & sqrt(z) < 4), ],
         hist(x)  )

>
> or
>
> plot(x,y) for x>0 .and. y>0 .and.z**2 > 100

The strategy generalizes.

>
> I cant find this simple task in a first perusal of some of the  
> tutorials.

>  Any suggestions you could give would be helpful.

Don't forget to read the Posting Guide.
>

-- 
David.