哪位同学能帮一下啊？poly2nb出现错误

同学们，为什么chn_nb=poly2nb("chn_poly")出现如下提示的错误呢？
chn_poly <- readShapePoly("CHN_adm1.shp")
chn_nb=poly2nb("chn_poly")

Error: extends(class(pl), "SpatialPolygons") is not TRUE


谁能帮忙看看啊


所需要的数据文件见下
CHN_adm.zip (5.32 MB) 本附件包括：

• CHN_adm1.dbf
• CHN_adm1.prj
• CHN_adm1.sbn
• CHN_adm1.sbx
• CHN_adm1.shp
• CHN_adm1.shx

2013-11-7 13:28:52 上传

chn_nb <- poly2nb("chn_poly")
改为
chn_nb <- poly2nb(chn_poly)

1. > chn_nb <- poly2nb(chn_poly)
   
2. > chn_nb
   
3. Neighbour list object:
   
4. Number of regions: 32
   
5. Number of nonzero links: 136
   
6. Percentage nonzero weights: 13.28125
   
7. Average number of links: 4.25
   
8. 2 regions with no links:
   
9. 8 20

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