Pandas sort dataframe using custom function

sort_df.py

def sort_df(df, column_idx, key):
    '''Takes dataframe, column index and custom function for sorting, 
    returns dataframe sorted by this column using this function'''
    
    col = df.ix[:,column_idx]
    temp = pd.DataFrame([])
    temp[0] = col
    temp[1] = df.index
    temp = temp.values.tolist()
    df = df.ix[[i[1] for i in sorted(temp, key=key)]]
    
    return df

Shorter version:

def sort_df(df, column_idx, key):
    '''Takes dataframe, column index and custom function for sorting, 
    returns dataframe sorted by this column using this function'''
    
    col = df.ix[:,column_idx]
    temp = np.array(col.values.tolist())
    order = sorted(range(len(temp)), key=lambda j: key(temp[j]))
    return df.ix[order]

.ix is deprecated

def sort_df(df, column_idx, key):
    '''Takes dataframe, column index and custom function for sorting, 
    returns dataframe sorted by this column using this function'''
    
    col = df.iloc[:,column_idx]
    temp = np.array(col.values.tolist())
    order = sorted(range(len(temp)), key=lambda j: key(temp[j]))
    return df.iloc[order]