loc: only work on index
iloc: work on position
ix: You can get data from dataframe without it being in the index
at: get scalar values. It‘s a very fast loc
iat: Get scalar values. It‘s a very fast iloc
pandas中Loc vs. iloc vs. ix vs. at vs. iat?
原文：http://www.cnblogs.com/coskaka/p/6107372.html