Els,
To add to what Carsten says: in that case you can use 'reclass' or 'subs'
 or (at least in current versions) replacement:  ndvi.stack[ndvi.stack ==
-0.3] <- NA
Robert


On Tue, Nov 8, 2011 at 4:14 AM, Carsten Neumann <carstennh@aol.com> wrote:

>  Am 08.11.2011 09:18, schrieb Els Ducheyne:
>
>  Dear list
>> I have been working with raster stack for a while. Until now I have not
>> experienced any problems with NAvalues on stacks. However, yesterday I was
>> stacking 6 layers in a stack. 4 of these seemed to contain background
>> values only with a value of -0.3.
>> I have tried to set the NAvalue on the stack as follows
>> NAvalues(ndvi.stack)<-  -0.3
>>
>> but when using summarise(ndvi.stack,na.rm=T) I still get the -0.3 values.
>> The main problem is that I am calculating monthly means after this step
>> as follows
>> monthly.mean<- calc(ndvi.stack,fun=mean,na.**rm=T) and that because of
>> the fact that the NA value is not accepted i get wrong outputs.
>>
>> is the NAvalue not accepted because the entire image is -0.3? or is there
>> another reason?
>>
>> i am using the Raster package version 1.9-5
>> Thanks for any suggestions
>> Best regards
>> Els
>>
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>>
> Dear Els,
>
> did you keep your dataset 'ndvi.stack' as read from disk? The function
> Navalues can only change values when reading your rasterStack object from
> disk. If you have your values in memory nothing will change applying your
> function.
>
> Maybe this could help?
>
> Best regards
>
> Carsten
>
> --
>
> Carsten Neumann
> Telegrafenberg, A 17 01.13
> 14473 Potsdam
> ------------------------------**-------------------------
> Helmholtz Centre Potsdam
> GFZ German Research Centre for Geosciences
> Department 1 - Section 1.4 - Remote Sensing
> ------------------------------**-------------------------
> Tel.: +49 (0) 331 288 1766
> e-mail: carstenn@gfz-potsdam.de
>
>
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