fixing one error + one repetition

"Names" is used as index so it could not be used in the example, I replaced it with another column name.
There was a repetition of the same set command and I removed it.

Author: eglerean

content/pandas.rst

@@ -129,12 +129,11 @@ refer to columns and rows either by number or by their name
 :attr:`~pandas.DataFrame.at`, :attr:`~pandas.DataFrame.iat`)::
 
     titanic.loc['Lam, Mr. Ali',"Age"]          # select single value by row and column
-    titanic.loc[:'Lam, Mr. Ali',"Name":"Age"]  # slice the dataframe by row and column *names*
+    titanic.loc[:'Lam, Mr. Ali',"Survived":"Age"]  # slice the dataframe by row and column *names*
     titanic.iloc[0:2,3:6]                      # same slice as above by row and column *numbers*
 
     titanic.at['Lam, Mr. Ali',"Age"] = 42      # set single value by row and column *name* (fast)
     titanic.at['Lam, Mr. Ali',"Age"]           # select single value by row and column *name* (fast)
-    titanic.at['Lam, Mr. Ali',"Age"] = 42      # set single value by row and column *name* (fast)
     titanic.iat[0,5]                           # select same value by row and column *number* (fast)
 
     titanic["is_passenger"] = True             # set a whole column