Concise notes¶

eval Function

The eval() function evaluates the specified expression (code), and runs it. The syntax is as below

Global variables in imported module

If you want to handle a global variable in an imported module, simply add it to the builtin module. Let's assume that VAR is a global variable in the fun1 function within the test module:

import builtins
import test
builtins.VAR = 3
test.fun1()

How generate variable name using loop item

If you need to create the variable name using the loop object, use exec.

How run apply on array

import numpy as np
x = np.array([[5,2,1,3], [2,1,5]])
fun = lambda t: np.argmax(t)
np.array([fun(xi) for xi in x])

Applying function on data-frame

Using df.apply(fun) can apply a function on columns or row:

Cheat Sheet of python core, Numpy, and Panda

Primer

Here and a brief of Useful functions of python core, Numpy and Panda are presented.

Cheat Sheet of Sklearn

Sklearn

Sklearn is built for general machine learning.

Crosstab

To show how generate the cross tabulate, let us categorize the columns; consider two continuous variables ( e.g., housing_median_age and total_rooms), categorize them according their .3 and .7 quantiles, and label the elements as L, M, and H. Then find the cross tabulate of them,

Data control structure

Boolean value

The value True (T) and False (F) are referred to as logical values and used the same in Python; their corresponding values are 1 and 0. Run the following codes and explains what the codes do.

Data-frame

Data-frame via pandas is very useful format for working with dataset, its structure is two-dimensional size-mutable, potentially heterogeneous tabular data structure with labeled axes (rows and columns). The following codes create a data-frame from a dictionary.