title: Select non-null rows from a specific column in a DataFrame and take a sub-selection of other columns
body: <p>I have a dataFrame which has several coulmns, so i choosed some of its coulmns to create a variable like this <code>xtrain = df[['Age','Fare', 'Group_Size','deck', 'Pclass', 'Title' ]]</code> i want to drop from these coulmns all raws that the Survive coulmn in the main dataFrame is nan.</p>