Adding new column to existing DataFrame in Python pandas

Question

I have the following indexed DataFrame with named columns and rows not- continuous numbers:

          a         b         c         d
2  0.671399  0.101208 -         


        

Answer 1

Before assigning a new column, if you have indexed data, you need to sort the index. At least in my case I had to:

data.set_index(['index_column'], inplace=True)
"if index is unsorted, assignment of a new column will fail"        
data.sort_index(inplace = True)
data.loc['index_value1', 'column_y'] = np.random.randn(data.loc['index_value1', 'column_x'].shape[0])