Error with RGEOS

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Just for dissolving I use the rgeos package with gUnaryUnion. But I get
this error :No UnaryUnion in this version of GEOS. I remove the package and
install it again but I get the same error. Is it linked to my version of R
or something else? This my code:

    require("rgeos")
    summary(utah) #
    regional= gUnaryUnion(utah,utah$region)


According to your suggestion I ask my question with more details:

For my R version:
R version 3.0.2 (2013-09-25) -- "Frisbee Sailing"
Copyright (C) 2013 The R Foundation for Statistical Computing
Platform: i686-pc-linux-gnu (32-bit)

From library (rgeos) I get this warning :

rgeos version: 0.3-6, (SVN revision 450)
GEOS runtime version: 3.2.2-CAPI-1.6.2

So your GEOS is 3.2.2, released March 2010, and as I wrote before, 
gUnaryUnion() is only available from GEOS 3.3.0.

Did you yourself install GEOS, or did someone else? Do you have multiple 
copies of GEOS installed to match other applications (PostGIS, QGIS), and 
have muddle in the search order of shared objects? Which GEOS was fould 
when rgeos was installed (it is reported to the console during 
installation)?

Did you try what I suggested, gUnionCascaded()? It does the same as 
gUnaryUnion(), but less efficiently. If you need gUnaryUnion(), upgrade 
GEOS to at least 3.3.0, and re-install rgeos.

Please do try to adhere to the instructions and posting guide for R 
lists, linked from the list page whose address is appended to every 
message published.

Roger

Polygon checking: TRUE


Thank you

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Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: Roger.Bivand at nhh.no