R help - Jun 2014 - Problem with converting a list of grids to a list of polygons

Hi. 

For a spatial analysis (its visualization) I need to produce a map of
conditions and traits. 
When I used SpatialPixelsDataFrame (sp package) my grid cells were regular
and between each row was a small gap, which is not only messy but incorrect.
So I generated the coords of each grid from the centroids in order to
elongate the cells manually (or does anybody know another way to solve
this?). 

But I got stuck when I tried to convert the XMIN, XMAX, YMIN, YMAX - corner
points to a list of polygons (and keeping at least the ID as individuell
reference). 


I really don?t get it, how can I read data of this format as a list of
polygons? 
?head"(ID, XMIN, XMAX, YMIN, YMAX,  lat, lng, altc_mean) 

polys <- Polygons(list(Polygon(assemblage[,c("XMIN",
"XMAX", "YMIN",
"YMAX?)])), ID=assemblage$ID) 
SP <- SpatialPolygons(polys) 
SPDF <- SpatialPolygonsDataFrame(SP, data=data.frame(x= assemblage$lng,
yassemblage$lat, row.names=row.names(SP)))




Already thanks for your help, 
Stefan         



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