R help - May 2012 - confused with indexing

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]]

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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