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In Class Activity - Python - More for-loops

Problem 0: A more complex for-loop over a dictionary

Here is a dictionary purchases that records a series of purchases, broken down into different categories. Each category is a list of the relevant purchases under that category.

purchases = {}
purchases['entertainment'] = [100., 50.50, 22.12]
purchases['food'] = [5.45, 1.20, 65.20, 5.99, 12.23]
purchases['transportation'] = [24.20, 26.11, 5.03]

Write a nested for-loop to compute the total cost of all the purchases. Alternatively, you can use the python sum function and a single for-loop.

# your answer goes here
total = 0.
for k in purchases.keys():
    mylist = purchases[k]
    for l in mylist:
        total += l
total

# OR
total = 0.
for k in purchases.keys():
    total += sum(purchases[k])
total

Problem 1: Using numpy

The code below imports numpy and creates a random matrix A with 5 rows and 4 columns. The entries in A are uniform random samples from \(0,\dots,2\).

import numpy as np
import numpy.random as npr

A = npr.randint(0,3,size=(5,4))
A

Use numpy to compute the sum of each column (google the numpy function for sum)

# Your answer here
np.sum(A,axis=0)

Use numpy to compute the sum of each row

# Your answer here
np.sum(A, axis=1)

Use numpy to compute the overall sum across the entirem atrix

# Your answer here
np.sum(A)