hierarchical indexing is an important feature of pandas enabling you to have multiple (two or moreindex levels on an axis somewhat abstractlyit provides way for you to work with higher dimensional data in lower dimensional form let' start with simple examplecreate series with list of lists or arrays as the indexin [ ]data series(np random randn( )index=[[' '' '' '' '' '' '' '' '' '' '][ ]]in [ ]data out[ ] - - - - - - what you're seeing is prettified view of series with multiindex as its index the "gapsin the index display mean "use the label directly above"in [ ]data index out[ ]multiindex [(' ' (' ' (' ' (' ' (' ' (' ' (' ' (' ' (' ' (' ' )with hierarchically-indexed objectso-called partial indexing is possibleenabling you to concisely select subsets of the datain [ ]data[' 'out[ ] - - - in [ ]data[' ':' 'out[ ] - - - - - in [ ]data ix[[' '' ']out[ ] - - - selection is even possible in some cases from an "innerlevelin [ ]data[: out[ ] hierarchical indexing www it-ebooks info