Extract Raster from Raster using Polygon shapefile in R

I am new to R and using the raster package. I have a problem extracting polygons from an existing raster file. If I use

extract(raster, poly_shape)

function on the raster it always creates a list with the data. What I really want is to extract another raster file that I can load with ArcGIS again. After reading a bit more I think the crop function is what I really need. But when I try to use this function

crop(raster, poly_shape)

I get this Error:

Error in .local(x, y, ...) : extents do not overlap

In addition: Warning message:
In intersect(extent(x), extent(y)) : Objects do not overlap

The files raster and poly_shape are the same for both functions. Can you tell me what could be wrong here? Is it even right that the crop function creates another raster and not a list?

EDIT: The extent() function does not work for me. I still get the same error. But I am sure the 2 datasets overlap! With the

extract(raster, poly_shape)

I get the right data from it. Just as a list and not as a raster like I want to have it. I just loaded the datasets in ArcGIS before and they fit very well so I did not check the projection. Now I tried

projection(raster) # "+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs"
projection(poly_shape) # "+proj=utm +zone=32 +ellps=GRS80 +units=m +no_defs"

and you can see that the projections do not fit. The extract function seems to be able to automatically transform the files in the right way. I know that because I did the following:

• I cut out the exact part of the polygon I extracted in R also in ArcGIS


• I calculated the sum of all values of the extracted R polygon (list)


• I calculated the sum of all raster cells that I cut out in ArcGIS

The 2 have the exact same result so I guess the conclusion should be that the extract function did work correct. Now I have 2 options I guess:

1. I need a way to get a Raster out of the extracted list again or



2. The 2 datasets (raster + poly_shape) need to use the same prjection and the crop function should work

What would you suggest to do here?

Answer

What I actually searched for was the mask() function.

mask(raster, poly_shape)

works without errors and returns what I searched for.