[R] confused with indexing

[Jim Holtman]

use is.null for the test

if (is.null(indexSkipped))

Sent from my iPad

On May 22, 2012, at 2:10, Alaios <alaios at yahoo.com> wrote:

> Dear all,
> I have a code that looks like the following (I am sorry that this is not a reproducible example)
> 
> 
>     indexSkipped<-NULL
> 
> 
> 
>  ....code Skipped that might alter indexSkipped
> 
> 
>     if (length(indexSkipped)==0)
>         spatial_structure<-spatial_structures_from_measurements(DataList[[i]]$Lon,DataList[[i]]$Lat,meanVector) 
>     else
>         spatial_structure<-spatial_structures_from_measurements(DataList[[i]]$Lon[-indexSkipped],DataList[[i]]$Lat[-indexSkipped],meanVector) # 
> 
> 
> 
> What I am doing here is that I am processing files. Every files has a measurement table and Longtitude and Latitude fields. If one file is marked as invalid I keep a number of of the skipped index so to remove the element of the Longtitude and Latitide vectors.
> 
> 1) That works correct, I was just wondering if it would be possible to remove some how the given if statement and initialize the indexSkipped in such a way so 
> 
> the DataList[[i]]$Lon[-indexSkipped],DataList[[i]]$Lat[-indexSkipped] do nothing, aka remove no element, in case the indexSkipped remains unchanged (in its initial value).
> 
> 2) When u define a variable as empty, I usually use NULL, how I can check afterwords if that holds or not. If I use  the 
> 
>  (indexSkipped==NULL)
> logical(0)
> 
> this does not return true or false. How I can do that check?
> 
> 
> Iwould like to thank you in advance for your help
> 
> B.R
> Alex
>    [[alternative HTML version deleted]]
> 
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