Description

• Reading from a file
• for loops
• Processing data in a file with split
• Building lists

Notes

You must save all your code as a script (use the interactive console to test your expressions, but save them in a file).

Grading

Total marks is 2.

You will receive 1 mark for attendence only if you stay until the end. If you have completed exercise 1 and 2 before the start of the lab, you can use the lab time to work on bonus question. You will either receive 0 or 1 mark for attendence.

Note – You do not have to successfully complete bonus question to get the attendence mark.

You will receive 1 mark for correct solutions to Exercise 1 and 2. You will have to demonstrate your program to the teaching assistant. You will receive 0.5 for each exercise. Use only what have been taught in class or described in this lab.

Important We highly recommend that you try to do the lab questions 1,2 before the start of your lab. Use the lab time to ask for help if you get stuck.

Exercises

Exercise 1: Standard deviation

Open the file lab4.csv. This file has 3 numbers per-line, separated by commas.

Calculate the mean and standard deviation of each column of the file, using the formula:

$$\sigma =\sqrt{\frac{{\sum }_{i=1}^N(x_i-\overline{x}{)}^2}{N-1}}$$

Where $\sigma$ is standard deviation, $\overline{x}$ is the mean of the dataset, $N$ is the number of elements in the dataset, and $x_i$ is an element of the dataset at spot $i$.

You will need to:

1. open the file.
2. Initialize 3 list accumulators.
3. Iterate over the lines of the file in a for loop and accumulate the values in the columns.
4. Compute the average (either do this inside the loop with a running sum or use the sum function on your lists).

Once you have the mean $\overline{x}$, calculate the standard deviation using a second for loop.

Your output should look like:

The mean of column 1 is 50.30, and the standard deviation is 28.81
The mean of column 2 is 499.79, and the standard deviation is 290.16
The mean of column 3 is 5011.12, and the standard deviation is 2874.15

Nested 🐤 lists

As an extra exercise, consider how to write this using nested lists. You may need to use the range function if you choose to solve this problem.

Exercise 2: Standard deviations from the mean

Add to your program from the previous part to ask for numerical input from the user. Find how many standard deviations from the mean the input is.

The formula for deviations from the mean is:

$$\text{deviationsFromMean}=\frac{|\overline{x}-x|}{\sigma }$$

Where $\sigma$ is the standard deviation, $\overline{x}$ is the mean of the dataset, and $x$ is the data the user provided.

Give me a number : > 50
This number is 0000.0104 standard deviations from the mean for column 1.
This number is 0001.5501 standard deviations from the mean for column 2.
This number is 0001.7261 standard deviations from the mean for column 3.

Nested 🐤 lists

If you did the extra exercise for above, add to this part an option for the user to choose which column the standard deviation is calculated for.

Optional exercises

Basic if usage

Change your above code. Use an if statement to remove negative numbers, creating a standard deviation with only positive numbers (which we will define as greater than or equal to 0).

Evens only

Change your if statement to only accept even numbers and positive. The data are decimal numbers, so we will define ‘even’ as “The 1s place is even”.

Saving your work

Save the files to the H: (Home) drive on your lab computer if you can; otherwise use the desktop or a USB drive. The desktop on a lab computer is stored on the computer itself, not on your network drive, so you should copy your files to a more permanent location before you leave. A good approach is to carry a thumb drive and plug it into the lab computer, using it to store your programs. Remember to take it with you!

Or, students have access to cloud storage (OneDrive), accessible through your @myumanitoba account. Log in at http://365.myumanitoba.ca. Once logged in, click on the App Launcher at the top left hand side and select OneDrive. To save a file, simply drag it to the OneDrive screen.