Lambda expression replaces anonymous classes and removes all boiler plate, enabling you to write code in functional style, which is some time more readable and expression.

Lambda Expression vs Anonymous class

1. Keyword this. For anonymous class this keyword resolves to anonymous class, whereas for lambda expression this keyword resolves to enclosing class where lambda is written.
2. The compiled way. Java compiler compiles lambda expressions and convert them into private method of the class.

Sort in non-standard way

In python2

>>> a = ['floor', 'house', 'room', 'roof']
>>> a.sort(lambda x,y: cmp(len(x), len(y)))
>>> a
['room', 'roof', 'floor', 'house']
>>>

In Python3

>>> a = ['floor', 'house', 'room', 'roof']
>>> a.sort(key=lambda x: (len(x)))
>>> a
['room', 'roof', 'floor', 'house']
>>>

Closures - functions evaluated in an environment containing bound variables

In python2

>>> def comp(threshold):
...     return lambda x: x < threshold
...
>>> func_a = comp(10)
>>> func_b = comp(20)
>>> print func_a(5), func_a(9), func_a(15), func_a(25)
True True False False
>>> print func_b(5), func_b(9), func_b(15), func_b(25)
True True True False

In python3

>>> def comp(threshold):
...     return lambda x: x < threshold
...
>>> func_a = comp(10)
>>> func_b = comp(20)
>>> print(func_a(5), func_a(9), func_a(15), func_a(25))
True True False False
>>> print(func_b(5), func_b(9), func_b(15), func_b(25))
True True True False

Mapping - performs a function call on each element of a list.

In python2

>>> a = [1, 2, 3, 4, 5, 6]
>>> print map(lambda x: x*x, a)
[1, 4, 9, 16, 25, 36]

In python3

>>> a = [1, 2, 3, 4, 5, 6]
>>> [item for item in map(lambda x: x*x, a)]
[1, 4, 9, 16, 25, 36]

Filter - returns all elements from a list that evaluate True when passed to a certain function.

In python2

>>> a = [1, 2, 3, 4, 5, 6]
>>> filter(lambda x: x % 2 == 0, a)
[2, 4, 6]

In python3

>>> a = [1, 2, 3, 4, 5, 6]
>>> list(filter(lambda x: x % 2 == 0, a))
[2, 4, 6]

Reduce - The fold/reduce function runs over all elements in a list (usually left-to-right), accumulating a value as it goes.

>>> from functools import reduce
>>> a = [1, 2, 3, 4, 5, 6]
>>> reduce(lambda x, y: x+y, a)
21
>>>

This performs (((((1 + 2) + 3) + 4) + 5) + 6) = 21

Install pymongo

pip install pymongo

The OS module in Python provides functions to using operating system dependent functionality.
To use it, import the OS module “import os”

Solution on Ubuntu:
Using the following command and find with process is holding the dataset.

grep zroot/2013-10-15T065955229209 /proc/*/mounts

note: replace zroot/2013-10-15T065955229209 as your mount point.

MongoDB provides four packages

YUM: Yellowdog Updater Modified

• Install a package with YUM:

  sudo yum install <package name>
  sudo yum -y install <package name>
  

Edit ~/.bashrc

http_proxy=http://yourproxyaddress:prosyport
export http_proxy

It the proxy server requires login, using the following configuration

http_proxy=http://username:password@yourproxyaddress:proxyprot
export http_proxy

Chrome can use fonts over internet. There are a lot fonts we can use. I installed custom fonts because I couldn’t find a way let chrome to use Nerd Fonts over internet.

Create OS Recovery Media

1. Insert a USB stick 4GB or greater
2. Install Chromebook Recovery Utility extension for chrome browser
3. Launch Chromebook Recovery Utility and follow the guide to create OS Recovery Media