Week 3

• Read in data from a .csv file (comma separated variables)

import numpy as np
data = np.loadtxt('path_to_csv/csv_name.csv', delimiter = ',')

Generate heatmap:

import matplotlib.pyplot as plt
plt.imshow(data)
plt.colorbar()
plt.ylabel('y label')
plt.xlabel('x label')

np.arange(x,y,z)

Produces a range from value x up to but not including y, counting by z

import numpy as np
print(np.arange(2,15))
print(np.arange(0,10,2))
print(np.arange(5,1,-1))

[ 2  3  4  5  6  7  8  9 10 11 12 13 14]
[0 2 4 6 8]
[5 4 3 2]

np.mean()

Takes the mean of an array or across the rows or column np.mean(array) returns the mean of all values in the array np.mean(array, axis = 0) takes the mean of each column np.mean(array, axis = 1) takes the mean of each row

Note: don't forget to check the shape of your output array to be sure you took the mean of the dimension you wanted.

np.max(), np.min(), and np.sum() function in the same way

np.zeros(n), np.ones(n)

Create an array of zeros or ones of length n

import numpy as np

print(np.zeros(7))
print(np.ones(5))
print(np.ones(5)+3)

[0. 0. 0. 0. 0. 0. 0.]
[1. 1. 1. 1. 1.]
[4. 4. 4. 4. 4.]

Plotting: Scatter plots, etc.

• Create a scatter plot:
  
  plt.scatter(x, y, color = , marker = , etc.)
  
  

For-loops

Structure:
for <variable> in <iterable object>:
do action

Anything indented will be contained in the loop

odds=[1,3,5,7]    # Define list (iterable)
for num in odds:  # For each variable (called num) in odds, do:
    print(num)    # Action (print the variable)

1
3
5
7

odds=[1,3,5,7]    
for anything in odds:  # the iterable variable can be called anything you want
    print(anything)

1
3
5
7

odds=[1,3,5,7]    
for num in odds:  
    print('loop')   # The action doesn't need to necessarily use the variable.
                    # in this case, the action (print('loop')) is performed as many times as there are variables in the list

loop
loop
loop
loop

Appending to lists:

odds=[1,3,5,7]    
more_odds = odds + [9]
print(more_odds)

[1, 3, 5, 7, 9]

more_odds.append(11) # Note you don't have to assign more_odds.append() to a new variable, more_odds is automatically updated with .append()
print(more_odds)     # In fact, if you run this cell a few more times, it will continue to append

[1, 3, 5, 7, 9, 11]

Creating a counter for a for-loop:

counter = 0
for i in range(0,5):
    print('loop ', counter)
    counter += 1              # This notation += is shorthand for "counter = counter + 1"

loop  0
loop  1
loop  2
loop  3
loop  4

enumerate():

enumerate() automatically creates a counter by generating an 'enumerate object' of the format [(0, item[0]), etc.]

my_list = ['alpha', 'bravo', 'charlie', 'delta', 'echo']
print(list(enumerate(my_list)))

[(0, 'alpha'), (1, 'bravo'), (2, 'charlie'), (3, 'delta'), (4, 'echo')]

You can assign the counter value and the list value to two variables so that they are both callable in the for-loop:

for counter, list_value in enumerate(my_list):
    print(counter)
    print(list_value)

0
alpha
1
bravo
2
charlie
3
delta
4
echo