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
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