[R] selecting subsets of data from matrix

[Laura Quinn]

Thanks for your help everyone,

My data is a matrix. However if i use the command:

x[(x[,20] > 315 | x[,20] < 45), ]

and then request a summary, I get a warning message saying that a large
number of the row names have been duplicated - I don't understand this?

On 20 Oct 2003, Douglas Bates wrote:

> Laura Quinn <laura at env.leeds.ac.uk> writes:
>
> > Probably a stupid question, but I don't seem to be able to find the answer
> > I'm looking for from any of the R literature. Basically I have a matrix
> > with several thousand rows and 20 columns(weather stations) of wind
> > direction data.
>
> Is it a matrix or a data frame?
>
> > I am wanting to extract a matrix which contains data for all columns
> > conditional on column 20 having a value of _either_ less than 45 or
> > greater than 315. (ie I want to extract a matrix which contains wind
> > direction data for all columns {weather stations} when there is a
> > prevailing northerly wind for one of the stations).
>
> > I have tried a few different methods of doing this, none with any success,
> > can anyone please advise?
>
> If x is a matrix they you want
>
>   mysubset <- x[x[,20] < 45 | x[,20] > 315,]
>
> If x is a data frame and column 20 is named col20 then you can use
>
>   mysubset <- subset(x, col20 < 45 | col20 >315)
>