I suspect I am trying to do something similar... I would like to create a mask where I have data. In essence, I need to return True where x,y is equal to lon,lat.... I suppose a setmember solution may somehow be more elegant, but this is what I've worked up for now... suggestions? def genDataMask(x,y, xbounds=(-180,180), ybounds=(-90,90), res=(0.5,0.5) ): """ generate a data mask no data = False data = True """ xy = numpy.column_stack((x,y)) newx = np.arange(xbounds[0],xbound[1],res[0]) newy = np.arange(ybounds[0],ybounds[1],res[1]) #create datamask dm = np.empty(len(newx),len(newy)) dm.fill(np.nan) for _xy in xy: dm[np.where(_xy[0]=newx),np.where(_xy[1]==newy) ] = True -- View this message in context: http://www.nabble.com/Masking-an-array-with-another-array-tp23185887p2494341... Sent from the Numpy-discussion mailing list archive at Nabble.com.