List Basic

x = [3,1,2]
print(x, x[2])
print(x[-1])
x[2] = 'foo'
x.append('bar')
print(x)
back = x.pop()
print(back,x)

[3, 1, 2] 2
2
[3, 1, 'foo', 'bar']
bar [3, 1, 'foo']

### Slicing

nums = list(range(5))
print(nums)
print(nums[2:4])
num = range(5)
print(num,type(num))
print(nums[2:])
print(nums[:2])
print(nums[:])
print(nums[:-1])
nums[2:4]=[8,9]
print(nums)

[0, 1, 2, 3, 4]
[2, 3]
range(0, 5) <class 'range'>
[2, 3, 4]
[0, 1]
[0, 1, 2, 3, 4]
[0, 1, 2, 3]
[0, 1, 8, 9, 4]

list_1 = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
print(list_1[:,1:3])

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-8-965a0a36bfb7> in <module>
      1 list_1 = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
----> 2 print(list_1[:,1:3])


TypeError: list indices must be integers or slices, not tuple

Loops

animals = ['cat', 'dog', 'monkey']
for animal in animals:
    print(animal)

cat
dog
monkey

for idx, animal in enumerate(animals):
    print('%d:%s' % (idx,animal))

cat
dog
monkey

List comprehensions

nums = [0,1,2,3,4]
squares = [ x**2 for x in nums]
print(squares)

[0, 1, 4, 9, 16]

nums = [[1,2,3],[4,5,6],[7,8,9]]
col_2 = [ row[2] for row in nums ]
print(col_2)

[3, 6, 9]

nums = [0,1,2,3,4,5,6]
squares = [ x**2 for x in nums if x%2 == 0 ]
print(squares)

[0, 4, 16, 36]

Dictionary Basic

d = {'cat':'cute', 'dog':'furry', 'fish':'yummy'}
print(d['dog'])
print('cat' in d)
d['banana'] = 'yellow'
print(d)
print(d.get('monkey', 'N/A'))
print(d.get('fish', 'N/A'))
del d['fish']
print(d.get('fish', 'N/A'))

furry
True
{'cat': 'cute', 'dog': 'furry', 'fish': 'yummy', 'banana': 'yellow'}
N/A
yummy
N/A

for key in d:
    print(key,d[key])

cat cute
dog furry
banana yellow

for key,val in d.items():
    print(key,val)

cat cute
dog furry
banana yellow

dictionary comprehensions

nums = [0,1,2,3,4,5]
square = { num:num*2 for num in nums}
print(square)

{0: 0, 1: 2, 2: 4, 3: 6, 4: 8, 5: 10}

Sets Basic

animals = {'cat', 'dog'}
print(animals)
print('cat' in animals)
print('fish' in animals)
animals.add('fish')
print('fish' in animals)
print(len(animals))
animals.add('cat')
print(len(animals))
animals.remove('cat')
print(len(animals))

{'dog', 'cat'}
True
False
True
3
3
2

animals = {'cat', 'dog','fish'}
for idx,animal in enumerate(animals):
    print(idx,animal)

dog
fish
cat

nums = [0,1,2,3,4,5]
square = { num for num in nums}
print(square)

{0, 1, 2, 3, 4, 5}

from math import sqrt
nums = {int(sqrt(i)) for i in range(30)}
print(nums)

{0, 1, 2, 3, 4, 5}

Tuples

nums = [0,1,2,3,4,5]
d = {(x-1,x):x+1 for x in nums }
print(d)

{(-1, 0): 1, (0, 1): 2, (1, 2): 3, (2, 3): 4, (3, 4): 5, (4, 5): 6}

t= (4,5)
print(type(t))
print(d[t])
print(d[(1,2)])

<class 'tuple'>
6
3

t = (1,2,3,4,5)
print(t[0:3])

(1, 2, 3)

List

List Basic Operation

select column from 2d list
```
y = [ x[col] for x in list ]
```
combine multiple list

y = [ [x1[col1],x2[col2],x3[col3]] for (x1,x2,x3) in zip (list1, list2, list3)]

append ```python
animals list

animals = [‘cat’, ‘dog’, ‘rabbit’]

list of wild animals

wild_animals = [‘tiger’, ‘fox’]

appending wild_animals list to the animals list

animals.append(wild_animals)

print(‘Updated animals list: ‘, animals) Output

```python
Updated animals list:  ['cat', 'dog', 'rabbit', ['tiger', 'fox']]

numpy.array and list conversion

list1 = array1.tolist()

array2 = np.array(list1)

Numpy.array()

create array

>>> arr = np.array([1,2,3,4,5])
>>> arr
array([1, 2, 3, 4, 5])
>>> print(arr)
[1 2 3 4 5]
>>> print(type(arr))
<class 'numpy.ndarray'>
>>> arr = np.array((1,2,3,4,5)).    #tuple as input
>>> arr
array([1, 2, 3, 4, 5])
>>> print(arr)
[1 2 3 4 5]
>>> print(type(arr))
<class 'numpy.ndarray'>
>>> arr = np.array([[1,2,3],[4,5,6]])       #2d array
>>> print(arr)
[[1 2 3]
 [4 5 6]]
>>> arr = np.array([[[1,2,3],[4,5,6]],[[1,2,3],[4,5,6]]])  #3d array
>>> print(arr)
[[[1 2 3]
  [4 5 6]]

 [[1 2 3]
  [4 5 6]]]
>>> print(arr.ndim)     #array dimension
3
>>> arr = np.array([1, 2, 3, 4], ndmin=5)
>>> print(arr)
[[[[[1 2 3 4]]]]]
>>> print(arr.ndim)
5
>>> np.array([1,2,3],dtype=complex)     #array type provided
array([1.+0.j, 2.+0.j, 3.+0.j])
>>> np.arange(10)      #using arange()
array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
>>> np.zeros((2,3))   #using zeros()
array([[0., 0., 0.],
       [0., 0., 0.]])
>>> np.arange(2,10,dtype=float)
array([2., 3., 4., 5., 6., 7., 8., 9.])
>>> np.arange(2,3,0.3)
array([2. , 2.3, 2.6, 2.9])
>>> np.linspace(1,10,3). #with specified number of elements
array([ 1. ,  5.5, 10. ])
>>> np.linspace(1,10,5)
array([ 1.  ,  3.25,  5.5 ,  7.75, 10.  ])

array indice ```python

i,j=np.indices((2,3)) i array([[0, 0, 0], [1, 1, 1]]) j array([[0, 1, 2], [0, 1, 2]]) M = 2i + 3j M array([[0, 3, 6], [2, 5, 8]])

np.indices((2,3)) array([[[0, 0, 0], [1, 1, 1]],

   [[0, 1, 2],
    [0, 1, 2]]]) ```

array zeros ```python

## Array basic operation

* transpose array
```python 
arr = array.T

Array Index

Single Index

>>> import numpy as np
>>> x = np.arange(10)
>>> x[2]
2
>>> x[0]
0
>>> x[10]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: index 10 is out of bounds for axis 0 with size 10
>>> x[9]
9
>>> x[-2]
8

array Dimension

list dimension

dim1 = len(list)
dim2 = len(list[0])
dim3 = len(list[1])

count

>>> array = np.array([1,1,1,2,2,3])
>>> array
array([1, 1, 1, 2, 2, 3])
>>> unique, counts = np.unique(array, return_counts=True)
>>> unique
array([1, 2, 3])
>>> counts
array([3, 2, 1])