[R] a question on subset a dataset

[Petr Pikal]

Hi

I coords was data frame you could use some arithmetic to get 
selection criteria for both numbers odd. In case of matrix you need 
to use coords[,1]*coords[,2] instead

trunc((coords$x*coords$y)/2)!=((coords$x*coords$y)/2)
[1]  TRUE FALSE  TRUE FALSE FALSE FALSE  TRUE FALSE  TRUE
coords[trunc((coords$x*coords$y)/2)!=((coords$x*coords$y)/2),]
 
HTH
Petr



On 13 Apr 2006 at 16:33, zhijie zhang wrote:

Date sent:      	Thu, 13 Apr 2006 16:33:52 +0800
From:           	"zhijie zhang" <epistat at gmail.com>
To:             	r-help at stat.math.ethz.ch
Subject:        	[R] a question on subset a dataset

> Dear R-users,
>  I generate a dataset "d", and want to get a subset from it.
> **
> *z<-rnorm(9)
> coords<-cbind(x=c(1,1,1,2,2,2,3,3,3),y=c(1,2,3,1,2,3,1,2,3))
> d<-SpatialPointsDataFrame(coords, data.frame (z=z[1:9]))*
> The result*/dataset* is
>   coordinates           z
> 1      (1, 1)  1.41173570
> 2      (1, 2)  0.18546503
> 3      (1, 3) -0.04369144
> 4      (2, 1) -0.21591338
> 5      (2, 2)  1.46377535
> 6      (2, 3)  0.22966664
> 7      (3, 1)  0.10762363
> 8      (3, 2) -1.37810256
> 9      (3, 3) - 0.96818288
>  Now I want oto get a subset with x(rows) and y(columns) being odd
>  numbers ,
> that is , i want the subset like the following:
>     coordinates           z
>     (1, 1)          1.41173570
>      (1, 3)        -0.04369144
>      (3, 1)         0.10762363
>     (3, 3)        -0.96818288
> I think that the steps maybe:
> 1.decompose coords into the original x and y;
> 2.select the odd numbers of x and y;
> 3.combine the selected x and y into coordinates, including the
> corresponding z-values. This is the subset.
>  Hope someone can solve it. I failed to get the subset.
> 
> 
> --
> Kind Regards,Zhi Jie,Zhang ,PHDDepartment of EpidemiologySchool of
> Public HealthFudan UniversityTel:86-21-54237149
> 
>  [[alternative HTML version deleted]]
> 
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Petr Pikal
petr.pikal at precheza.cz