i have a data set called "sales" which is a SFrame.
there's a column called "sqft\_living" and i want to convert it to log value. data type of column is float. but when i try to convert it with log() function it asks a float although its already a float.
here are the screenshot of codes and error. could you please help me to find the issue and convert the column to log 

```
a=train_data['sqft_living']
a

result of a
dtype: float
Rows: 17384
[1180.0, 2570.0, 770.0, 1960.0,...]

```

**this shows that "a" is float**

then i used below code to transform to log value in to new column called 'log\_sqft\_living' 

```
train_data['log_sqft_living']= log(a)

```

but it gives be below error

```
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-23-6de995ee575f> in <module>()
----> 1 train_data['log_sqft_living']= log(a)

TypeError: a float is required

```