["python","pandas","concatenation"]
pandas concat columns ignore_index doesn't work

I am trying to column-bind dataframes (like R's cbind() does) and having issue with pandas concat, as ignore_index=True doesn't seem to work: df1 = pd.DataFrame({'A': ['A0', 'A1', 'A2', 'A3'], 'B': ['B0', 'B1', 'B2', 'B3'], 'D': ['D0', 'D1', 'D2', 'D3']}, index=[0, 2, 3, 4]) df2 = pd.DataFrame({'A1': ['A4', 'A5', 'A6', 'A7'], 'C': ['C4', 'C5', 'C6', 'C7'], 'D2': ['D4', 'D5', 'D6', 'D7']}, index=[5, 6, 7, 3]) df1 # A B D # 0 A0 B0 D0 # 2 A1 B1 D1 # 3 A2 B2 D2 # 4 A3 B3 D3 df2 # A1 C D2 # 5 A4 C4 D4 # 6 A5 C5 D5 # 7 A6 C6 D6 # 3 A7 C7 D7 dfs = [df1, df2] df = pd.concat(dfs, axis=1, ignore_index=True) print df and the result is 0 1 2 3 4 5 0 A0 B0 D0 NaN NaN NaN 2 A1 B1 D1 NaN NaN NaN 3 A2 B2 D2 A7 C7 D7 4 A3 B3 D3 NaN NaN NaN 5 NaN NaN NaN A4 C4 D4 6 NaN NaN NaN A5 C5 D5 7 NaN NaN NaN A6 C6 D6 Even if I reset index using df1.reset_index() df2.reset_index() and then try pd.concat([df1, df2], axis=1) it still produces the same result! The expected result is a 6x4 dataframe where the contents of columns A,B,D, A1,C,D2 are horizontally concatenated.
If I understood you correctly, this is what you would like to do. import pandas as pd df1 = pd.DataFrame({'A': ['A0', 'A1', 'A2', 'A3'], 'B': ['B0', 'B1', 'B2', 'B3'], 'D': ['D0', 'D1', 'D2', 'D3']}, index=[0, 2, 3, 4]) df2 = pd.DataFrame({'A1': ['A4', 'A5', 'A6', 'A7'], 'C': ['C4', 'C5', 'C6', 'C7'], 'D2': ['D4', 'D5', 'D6', 'D7']}, index=[4, 5, 6 , 7]) df1.reset_index(drop=True, inplace=True) df2.reset_index(drop=True, inplace=True) df = pd.concat([df1, df2], axis=1) Which gives: A B D A1 C D2 0 A0 B0 D0 A4 C4 D4 1 A1 B1 D1 A5 C5 D5 2 A2 B2 D2 A6 C6 D6 3 A3 B3 D3 A7 C7 D7 Actually, I would have expected that df = pd.concat(dfs, axis=1, ignore_index=True) gives the same result. This is the excellent explanation from jreback: ignore_index=True ‘ignores’, meaning doesn’t align on the joining axis. it simply pastes them together in the order that they are passed, then reassigns a range for the actual index (e.g. range(len(index))) so the difference between joining on non-overlapping indexes (assume axis=1 in the example), is that with ignore_index=False (the default), you get the concat of the indexes, and with ignore_index=True you get a range.