Added as_id_array function.
Added as_id_array function.

Carralex/landlab,csherwood-usgs/landlab,laijingtao/landlab,cmshobe/landlab,SiccarPoint/landlab,cmshobe/landlab,ManuSchmi88/landlab,csherwood-usgs/landlab,SiccarPoint/landlab,RondaStrauch/landlab,RondaStrauch/landlab,amandersillinois/landlab,ManuSchmi88/landlab,Carralex/landlab,landlab/landlab,ManuSchmi88/landlab,landlab/landlab,RondaStrauch/landlab,laijingtao/landlab,cmshobe/landlab,Carralex/landlab,landlab/landlab,amandersillinois/landlab