How can I avoid repeated indices in pandas DataFrame after concat?

I have two pandas dataframes and concatenate them: ``` In[55]: adict = {'a':[0, 1]} bdict = {'a': [2, 3]} dfa = DataFrame(adict) dfb = DataFrame(bdict) dfab = pd.concat([dfa,dfb]) ``` The problem is, the resulting dataframe has repeated index. ``` In [56]: dfab.head() Out[56]: a 0 0 1 1 0 2 1 3 ``` How can I have a single index running through the resulting dataframe, i.e. ``` In [56]: dfab.head() Out[56]: a 0 0 1 1 2 2 3 3 ```