[SOLVED] Iti 1120 lab # 8 (2d) lists, matrices, files
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• A matrix is a two dimensional rectangular grid of numbers:
• The dimensions of the matrix are the numbers of rows and columns (in
the above case: row dimension 3, column dimension 3).
• A value within a matrix is referred to by its row and column indices, in that
order.
– Math: number rows and columns from 1, from upper left corner
• In math notation, M1,2 = 2
– In Python, matrices are implemented via 2D lists and indices start from
0, as they do in (1D) lists.
• Thus, M[0][1] is 2
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4 5 6
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Matrix element processing
• To visit every element of an array, we had to
use a loop.
• To visit every element of a matrix, we need to
use a loop inside a loop:
– Typically the outer loop goes through each row of
a matrix
– And the inner loop goes through each column
within one row of a matrix.
Intro to matrices in python
and programming exercises 1 to 5
Open a file called basics-2Dlists.py and spend time studying all the
matrix functions there.
The open the file called basics-2Dlists-todo.py and implement (and
test) the 5 functions labeled as programming exercise 1 to 5 in that
file.
Two notes about exercises 2 and 5:
• Q2: For clarification of programming exercise 2 see the next page
• Q5: In programming exercise 5, try to find a solution that does
not create any extra list. Or even better, find two solutions, one
that creates an extra list and one that does not
Details about Prog Ex 2
Find the sum of the upper triangle of a square
matrix (i.e. the diagonal and up).
1 4 5 3 2
6 3 6 4 6
M = 4 3 6 7 2
3 4 2 2 4
2 3 8 3 5
How do we know if an
element of a square
matrix is on or above
the main diagonal?
row_index <=
column_index
0 1 2 3 4
0
1
2
3
4
Programming exercise 6 : Magic square
An n x n matrix forms am magic square if the following
conditions are met
1.The elements of the matrix are numbers 1, 2, 3, …, n2
2.The sum of the elements in each row, in each column and in
the two diagonals is the same value
https://en.wikipedia.org/wiki/Magic_square
Open magic.py and complete the function that tests if the given
matrix m forms a magic square.
Learn how to populating a 2D list from a file
View the content of the file called alkaline_metals.txt
This file contains the name, atomic number, and atomic weight of the alkaline
earth metals separated by space. Records about different metals are separated
by new line.
The goal of this exercise is to learn how to write a Python program that opens
and reads that file and creates and populates a 2D lists with the relevant info
about the 6 alkaline metals. Specifically the program needs to have a function,
called create_alctable(file_name), that given a string representing
the name of the file as input, opens that file, reads it and returns the following
2D list:
[[‘beryllium’, 4, 9.012], [‘magnesium’, 12, 24.305],
[‘calcium’, 20, 20.078], [‘strontium’, 38, 87.62], [‘barium’,
56, 137.327], [‘radium’, 88, 226.0]]
Open working-with-files.py, that solves this problem. Press Run Module. When
prompted for the file name enter: alkaline_metals.txt
Study what the program prints and the solution code. The printouts should elp
you understand the code.
You will need to do something similar in the next programming exercise of this
lab and in your Assignment 4.
Programming exercise 7: NY times bestsellers
For this you are provided with 2 files NY_short.txt and NY_long.txt each containing
list of New York Times for some years. Each line in a file contains the information
for a separate book, which includes: title, author, publisher, date it first reached
#1 on one of the best seller lists, and category (fiction or nonfiction). There is a
tab character between each of these pieces of information.
For this exercise you will first write a function create_books_2Dlist(file_name)
that opens the file, reads it and returns a 2D lists containing a sublist with the info
about each book. For example here is the beginning of required 2D list. See the
next page for what the whole list should look like for
[[‘1976-04-11’, ‘1876’, ‘Gore Vidal’, ‘Random House’, ‘Fiction’], … ]
Note that within each (sub)list about a book, the first element should be a string
contaning the date in iso format
YYYY-MM-DD
Finally you should write a function called search_by_year(books,year1,year2)
that given a 2D list of books in the above format prints all the bestsellers from year
1 to year2. See example runs on the next 2 pages for NYT_short.txt
While working use NYT_short.txt. Once you are done you can test your program
with NYT_long.txt.
Programming exercise 7: example runs
Programming exercise 7: example runs
Below the books argument is the 2D lists from the previous slide
EXTRA programming exercise (Back to 1D lists)
Write a function called move_zeros that takes as input list of integers and moves all the zeros in that list to
the end of the list (without affecting the relative order of other numbers). For example, if the list was [1, 0,
3, 0, 0, 5, 7] the new changed list should be [1, 3, 5, 7, 0, 0, 0]
•Write THREE different solutions (Version 3 is challenging)
– move_zeros_v1 should create a second, tmp, list to build the result (easier problem) and return
that 2nd list. It should not change the given list.
– move_zeros_v2 modify the previous question so that the given list IS modified Inside of the
function (i.e. its zeros are at the end) . This function returns nothing.
– move_zeros_v3 You may change the relative order of other elements here. This version should be
moving elements in the same list without creating any additional lists (so called, in-place,
solutions). (harder problem) This function returns nothing. You can use one extra variable to store
one integer but even that is not necessary since in Python you can swap what variables a and b
refer to by doing a,b=b,a For both problems the TAs will first discuss algorithmic approaches
to solve the problems
>>> x = [1, 0, 3, 0, 0, 5, 7]
>>> y=move_zeros_v1(x)
>>> print(x, y)
[1, 0, 3, 0, 0, 5, 7] [1, 3, 5, 7, 0, 0, 0]
>>> x = [1, 0, 3, 0, 0, 5, 7]
>>> z=move_zeros_v2(x)
>>> print(x, z)
[1, 3, 5, 7, 0, 0, 0] None
>>> x = [1, 0, 3, 0, 0, 5, 7]
>>> t=move_zeros_v3(x)
>>> print(x, t)
[1, 7, 3, 5, 0, 0, 0] None