Log values by SFrame column

Question

Please, can anybody tell me, how I can take logarithm from every value in SFrame, graphlab (or DataFrame, pandas) column, without to iterate through the whole length of the SFrame column? I specially interest on similar functionality, like by Groupby Aggregators for the log-function. Couldn't find it someself...

Important: Please, I don't interest for the for-loop iteration for the whole length of the column. I only interest for specific function, which transform all values to the log-values for the whole column.

I'm also very sorry, if this function is in the manual. Please, just give me a link...

Answer 1

numpy provides implementations for a wide number of basic mathematical transformations. You can use those on all data structures that build on numpy's ndarray.

import pandas as pd
import numpy as np
data = pd.Series([np.exp(1), np.exp(2), np.exp(3)])
np.log(data)

Outputs:

0    1
1    2
2    3
dtype: float64

This example is for pandas data types, but it works for all data structures that are based on numpy arrays.

Answer 2

The same "apply" pattern works for SFrames as well. You could do:

import graphlab
import math

sf = graphlab.SFrame({'a': [1, 2, 3]})
sf['b'] = sf['a'].apply(lambda x: math.log(x))