Training data and models in Intro to Computing - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is training data in machine learning?

Training data is the set of examples used to teach a machine learning model how to make predictions or decisions. It contains input data and the correct answers (labels).

beginner

What is a model in the context of machine learning?

A model is a mathematical or computational representation that learns patterns from training data to make predictions or decisions on new data.

beginner

Why do we split data into training and testing sets?

We split data to train the model on one part (training set) and check how well it works on unseen data (testing set). This helps us know if the model can generalize well.

intermediate

What does it mean when a model is overfitting?

Overfitting happens when a model learns the training data too well, including noise or mistakes, so it performs poorly on new data.

intermediate

How does training data quality affect the model?

Good quality training data helps the model learn correct patterns. Poor quality data with errors or bias can lead to wrong or unfair predictions.

What is the main purpose of training data?

A To clean the data

B To test the model's accuracy

C To teach the model how to make predictions

D To store the final results

Training data is used to teach the model the relationship between inputs and outputs.

What do we call the part of data used to check model performance on new data?

A Testing set

B Validation set

C Training set

D Input set

The testing set is used to evaluate how well the model performs on unseen data.

Which problem occurs when a model fits training data too closely and fails on new data?

A Underfitting

B Overfitting

C Data cleaning

D Normalization

Overfitting means the model learned noise or details that don't generalize well.

What is a model in machine learning?

A A visualization chart

B A set of rules written by humans

C A database of training examples

D A mathematical representation learned from data

A model is a learned mathematical or computational representation that makes predictions.

Why is training data quality important?

A It ensures the model learns correct patterns

B It reduces file size

C It speeds up the computer

D It changes the model type

High-quality data helps the model learn accurate and fair patterns.

Explain in your own words what training data and a model are, and how they work together.

Think about how you learn from examples and then use that knowledge.

Describe why splitting data into training and testing sets is important for building a good model.

Consider how you check your understanding by practicing and then testing yourself.

Practice

1. What is the main purpose of training data in machine learning?

easy

A. To teach the model patterns and relationships in data

B. To test the model's accuracy after training

C. To store the final predictions of the model

D. To clean and prepare data for analysis

Solution

1. Step 1: Understand the role of training data

   Training data is used to show the model examples so it can learn patterns.

2. Step 2: Differentiate training from testing

   Testing data checks model accuracy, but training data teaches the model.

3. Final Answer:

   To teach the model patterns and relationships in data -> Option A

4. Quick Check:

   Training data = Teach model [OK]

Hint: Training data is what the model learns from [OK]

Common Mistakes:

• Confusing training data with testing data
• Thinking training data stores predictions
• Assuming training data is for cleaning only

2. Which of the following is the correct way to split data into training and testing sets in Python using scikit-learn?

easy

A. test_train_split(data, size=0.2)

B. train_test_split(data, test_size=0.2)

C. train_test(data, split=0.2)

D. split_train_test(data, 0.2)

Solution

1. Step 1: Recall the scikit-learn function name

   The correct function to split data is train_test_split.

2. Step 2: Check the parameter syntax

   The parameter test_size=0.2 correctly sets 20% data for testing.

3. Final Answer:

   train_test_split(data, test_size=0.2) -> Option B

4. Quick Check:

   Correct function and parameter = train_test_split(data, test_size=0.2) [OK]

Hint: Remember scikit-learn's function is train_test_split [OK]

Common Mistakes:

• Using wrong function names
• Mixing parameter names
• Incorrect order of arguments

3. Given the following Python code, what will be the output?

from sklearn.linear_model import LinearRegression
import numpy as np

X = np.array([[1], [2], [3], [4]])
y = np.array([2, 4, 6, 8])
model = LinearRegression()
model.fit(X, y)
pred = model.predict([[5]])
print(round(pred[0], 1))

medium

A. 9.0

B. 12.0

C. 8.0

D. 10.0

Solution

1. Step 1: Understand the training data relationship

   X values are 1 to 4, y values are double X (2,4,6,8), so model learns y = 2 * X.

2. Step 2: Predict for X=5 using the model

   Prediction = 2 * 5 = 10.0, rounding to 1 decimal is 10.0.

3. Final Answer:

   10.0 -> Option D

4. Quick Check:

   Prediction for 5 = 10.0 [OK]

Hint: Model learns y=2x, predict for 5 gives 10 [OK]

Common Mistakes:

• Ignoring rounding in output
• Misunderstanding model relationship
• Using wrong input shape for predict

4. Identify the error in this code snippet for training a model:

from sklearn.linear_model import LogisticRegression
X_train = [[0, 1], [1, 0]]
y_train = [0, 1]
model = LogisticRegression()
model.fit(y_train, X_train)

medium

A. The order of arguments in model.fit() is reversed

B. LogisticRegression cannot be used with this data

C. X_train should be a numpy array, not a list

D. y_train should contain strings, not integers

Solution

1. Step 1: Check the model.fit() argument order

   fit() expects features first (X_train), then labels (y_train).

2. Step 2: Identify the mistake in the code

   Code passes y_train first, then X_train, which is incorrect and causes error.

3. Final Answer:

   The order of arguments in model.fit() is reversed -> Option A

4. Quick Check:

   fit(X_train, y_train) correct order [OK]

Hint: fit() needs features first, labels second [OK]

Common Mistakes:

• Swapping X and y in fit()
• Assuming data type causes error here
• Thinking LogisticRegression needs string labels

5. You have a dataset with 1000 samples and 10 features. You want to train a model but avoid overfitting. Which approach helps most during training?

hard

A. Use all data for training without splitting

B. Train only on the first 100 samples

C. Split data into training and validation sets

D. Ignore feature scaling and train directly

Solution

1. Step 1: Understand overfitting and validation

   Overfitting happens when model learns training data too well and fails on new data.

2. Step 2: Use validation set to check model generalization

   Splitting data into training and validation helps detect and reduce overfitting.

3. Final Answer:

   Split data into training and validation sets -> Option C

4. Quick Check:

   Validation split prevents overfitting [OK]

Hint: Validation set helps check model generalization [OK]

Common Mistakes:

• Training on all data hides overfitting
• Using too few samples reduces learning
• Ignoring feature scaling can hurt model