How to loop over python dictionaries and Numpy arrays

As you can see, the dictionary contains key-value pairs of stock symbols and their prices. We can iterate over it and print each stock's information on a different line as follows (using for loop).

1for key, value in portfolio.items() :
2    print("The stock " + key + " has a price of " + str(value))
3

Results:

1The stock GOOGL has a price of 849
2The stock FB has a price of 136
3The stock MSFT has a price of 64
4The stock AAPL has a price of 136
5The stock AMZN has a price of 848
6

Loop Over Numpy Array (1d)

If we have a one-dimensional Numpy array, looping over it is easy. Consider the following Numpy array:

We can iterate over the elements as follows:

1import numpy as np
2prices = np.array([5,8,12.7,89.6,12.9,5.4])
3for price in prices :
4    print ("The price is: " + str(price))
5

Results:

1The price is: 5.0
2The price is: 8.0
3The price is: 12.7
4The price is: 89.6
5The price is: 12.9
6The price is: 5.4
7

Loop over Numpy Arrays (Multi-dimensional)

For multidimensional arrays, iteration proceeds over the first axis such that each loop returns a subsection of the array. Consider the following array:

1a = np.array([[ 1.,  2.,  3.],
2       [ 4.,  5.,  6.]])
3

The result will be:

1[ 1.  2.  3.]
2[ 4.  5.  6.]
3

However, if you wanted to iterate over each separate element of the multi-dimensional array, you can do so using the nditer() method as shown below:

This will print each element separately as shown below:

11.0
22.0
33.0
44.0
55.0
66.0
7

Let's take another example. Consider an array which contains original loan amounts and the balance principal outstanding on 5 different stocks. All figures are in '000.

1loan_summary = np.array([[25,10],[30,15],[30,18],[60,30],[40,7]])
2

Suppose we want to print the results in this manner - "Y principal outstanding on a loan of X". To do so, we can use multiple assignments as shown below:

1for (x, y) in loan_summary:
2    print (str(y) + " principal outstanding on a loan of " + str(x))
3

Results:

110 principal outstanding on a loan of 25
215 principal outstanding on a loan of 30
318 principal outstanding on a loan of 30
430 principal outstanding on a loan of 60
57 principal outstanding on a loan of 40
6

Exercise

Consider our loan example, but this time as a list with each item of the list containing three pieces of information: the borrower's name, the original loan amount, and the principal outstanding.

1# Loan details
2loans = [["John", 25,10],
3         ["Ken", 30,15],
4         ["Mat", 30,18],
5         ["Ron", 60,30],
6         ["David", 40,7]]
7

You need to build a for loop from scratch and print each loan's information in a separate line in this format - "'Name's took a loan of X. The outstanding balance is Y".

Hint: If your for loop is defined as:

1for loan in loans :
2    ...
3

You can use loan[0] to access the first element, loan[0] to access the second element and so on. Feel free to discuss the problem in the forum/comments.