Graphlab：替换Sframe中的值和过滤(Graphlab : replacing values in Sframe and filtering)

 所以我有这个非常愚蠢的问题，我已经磕了几个小时。 我正在练习kaggle的泰坦尼克号ML练习，使用graphlab创建。 
 
 我的数据如下所示：  
 
 现在我想替换表中的一些值。 例如，我想将（作为测试）年龄设置为38，对于Pclass == 1 30为Pclass == 2和26为Pclass == 3 
 
 我已经尝试了很多这样做的方法，我迷失了。 
 
 我现在所拥有的只是： 
 
df = gl.SFrame(data)
df[(df["Pclass"]==1)] #will print the rows of the table where Pclass=1
df["Age"][df["Pclass"]==1] #will display an array containg only the column "Age" for Pclass=1
 
 现在我正在尝试正确使用SFrame.apply，但我很困惑。 
 
 我试过了 
 
df["Age"][df["Pclass"]==1].apply(lambda x: 38)
 
 返回一个具有正确值的数组，但我无法将其应用于SFrame。 例如，我尝试过： 
 
df = df["Age"][df["Pclass"]==1].apply(lambda x: 38)
 
 但是现在我的DataFrame变成了一个列表......（显然） 
 
 我还尝试过： 
 
df["Age"] = df["Age"][df["Pclass"]==1].apply(lambda x: 38)
 
 但是我收到以下错误：“RuntimeError：Runtime Exception。Column”__PassengerId-Survived-Pclass-Sex-Age-Fare“的大小与当前列不同！” 
 
 我确信解决方案很简单，但我太困惑了，不能自己找到它。 
 
 最终我想要像df [“Age”] = something.apply（lambda x：38，如果Pclass == 1，其他30，如果Pclass == 2，则其他26，如果Pclass == 3） 
 
 谢谢。 

So I have this very stupid problem I have been stumbling upon for hours. I'm practicing on kaggle's Titanic ML exercice, using graphlab create.
 
My data is as shown below : 
 
Now I want to replace some values in the table. For example I want to set (as a test) the age to 38 for Pclass==1 30 for Pclass==2 and 26 for Pclass==3
 
I have tried so many ways of doing this that I am lost.
 
All I have now is : 
 
df = gl.SFrame(data)
df[(df["Pclass"]==1)] #will print the rows of the table where Pclass=1
df["Age"][df["Pclass"]==1] #will display an array containg only the column "Age" for Pclass=1
 
Now I am trying to use SFrame.apply properly but I'm confused.
 
I have tried 
 
df["Age"][df["Pclass"]==1].apply(lambda x: 38)
 
That returns an array with the correct values but I was not able to apply it to the SFrame. For example, I have tried : 
 
df = df["Age"][df["Pclass"]==1].apply(lambda x: 38)
 
But now my DataFrame has turned into a list ... (obviously)
 
Il have also tried : 
 
df["Age"] = df["Age"][df["Pclass"]==1].apply(lambda x: 38)
 
But I get the following error : "RuntimeError: Runtime Exception. Column "__PassengerId-Survived-Pclass-Sex-Age-Fare" has different size than current columns!"
 
I'm sure the solution is pretty simple but I am too confused to find it by myself.
 
Ultimately I would like something like df["Age"] = something.apply(lambda x: 38 if Pclass==1 else 30 if Pclass==2 else 26 if Pclass==3)
 
Thanks.