I might get the reason, I found some code in /pandas/io/formats/excel.py as below. While thegroupby() function in Pandas would work, this case is also an example of where a MultiIndex could come in handy. To start, I am going to create a sample DataFrame: pandas.MultiIndex. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Sometimes it’s just easier to work with a single-level index in a DataFrame. Example 1: Using single level dataframes for pandas melt() function. Index or MultiIndex. Teams. non-hierchical) indices. When as_level=False is on, some types of agg don't work. Replace NaN with this value if the unstack produces missing values. Something here doesn't quite gel for me! However, when exporting to CSV, sometimes it might be desirable to have only one header row. A MultiIndex can be created from a list of arrays (using MultiIndex.from_arrays()), an array of tuples (using MultiIndex.from_tuples()), a crossed set of iterables (using MultiIndex.from_product()), or a DataFrame (using MultiIndex.from_frame()). value_name : scalar,default value – This is the name used for value column. A MultiIndex, also known as a multi-level index or hierarchical index, allows you to have multiple columns acting as a row identifier, while having each index column related to another through a parent/child relationship. fill_value int, str or dict. Parameters level int, str, or list of these, default -1 (last level) Level(s) of index to unstack, can pass level name. sortlevel The MultiIndex object is the hierarchical analogue of the standard Index object which typically stores the axis labels in pandas objects. pandas.DataFrame(map(list,aaa.index.get_tuple_index()),columns=aaa.index.names) Maybe it is just me, but I just don't get what MultiIndex is trying to do :) I have them after groupby().agg. Q&A for Work. In this post, I’ll show you a trick to flatten out MultiIndex Pandas columns to create a single index DataFrame. I definitely see the merits, but it just doesn’t feel right within a machine learning and feature engineering context. Stacking and unstacking can also be applied to data with flat (i.e. Coming from R, I’m not a big fan of MultiIndex DataFrames in Pandas. pandas.MultiIndex.droplevel, If a string is given, must be the name of a level If list-like, elements must be names or indexes of levels. However, sometimes you will end up with a MultiIndex DataFrame, after some ninja line of code. AFAIK, there is no dedicated method to flatten an existing multi-index. For example, when pivoting data into a wide format, the new columns are generally multi-indexed. pandas.DataFrame.unstack ... (the analogue of stack when the columns are not a MultiIndex). In this example, the melt function of pandas is applied on single level dataframes. df.columns = ['A','B','C'] In : df Out: A B C 0 0.785806 -0.679039 0.513451 1 -0.337862 -0.350690 -1.423253 PDF - Download pandas for free Previous Next col_level : int or str, optional – If columns are a MultiIndex then use this level to melt. Returns. Therefore, the result is always a Series with a hierarchical index. In this case, one of the indices is de facto removed (the columns index if stacking, and the rows if unstacking) and its values are nested in the other index, which is now a MultiIndex. However I don't know how to fix this issue # MultiIndex columns require an extra row # with index names (blank if None) for # unambiguous round-trip, unless not merging, # in which case the names all go on one row Issue #11328 The Index constructor will attempt to return a MultiIndex when it is passed a list of tuples. Sometimes it is useful to flatten all levels of a multi-index.
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