Free MATLAB Data Types and Structures Questions and Answers — Questions and Answers
Question 1: An engineer needs to store data for multiple electronic components. Each component has a text-based part number (e.g., 'R-101'), a numeric resistance value (e.g., 4700), and a 1x2 vector for its physical dimensions (e.g., [0.25, 0.125]). Which data structure is most suitable for creating an array to hold all the information for 50 such components?
- A cell array
- A multidimensional numeric array
- A structure array (Correct answer)
- A table with mixed data types
Correct answer: A structure array
A structure array is ideal for this scenario. Each element of the array can be a struct representing one component, with named fields like 'PartNumber', 'Resistance', and 'Dimensions' holding the different data types. This keeps the related data for each component neatly organized.
Question 2: A data analyst has a list of experimental conditions stored in a string array: `conditions = ["Low", "Medium", "High", "Medium", "Low"];`. To improve memory efficiency and enable mathematical comparisons (e.g., 'Low' < 'Medium'), which data type conversion is most appropriate?
- Convert to a numeric array using `double()`
- Convert to a cell array of character vectors
- Convert to an ordinal `categorical` array (Correct answer)
- Convert to a `table` with one variable
Correct answer: Convert to an ordinal `categorical` array
Converting to an ordinal `categorical` array is the best choice. Categorical arrays are memory-efficient because they store integer pointers to a single copy of each unique category name. Specifying them as 'ordinal' allows for defining a mathematical order ('Low' < 'Medium' < 'High'), which is not possible with string or cell arrays.
Question 3: A programmer creates two text variables as follows:
`text1 = 'Results';`
`text2 = "Results";`
What are the data types (classes) of `text1` and `text2` respectively?
- `string` and `char`
- `char` and `string` (Correct answer)
- Both are `char`
- Both are `string`
Correct answer: `char` and `string`
In MATLAB, single quotes `' '` are used to create a character array (class `char`). Double quotes `" "` are used to create a string scalar or string array (class `string`). Therefore, `text1` is a `char` array and `text2` is a `string`.
Question 4: A programmer needs to create a single container variable that can hold the following three items: a 4x4 magic square, the character vector 'Experiment A', and a `datetime` object. Which of the following commands correctly creates such a container?
- C = [magic(4); 'Experiment A'; datetime('now')]
- C = {magic(4), 'Experiment A', datetime('now')} (Correct answer)
- C = struct('Data', magic(4), 'Name', 'Experiment A', 'Time', datetime('now'))
- C = table(magic(4), 'Experiment A', datetime('now'))
Correct answer: C = {magic(4), 'Experiment A', datetime('now')}
A cell array, created using curly braces `{}`, is the only data type among the choices that can store completely different data types and sizes (a 4x4 matrix, a 1x12 char array, and a 1x1 datetime object) as individual elements in a simple 1x3 array.
Question 5: Given a table `T` created with the command `T = table([8; 10; 11], ["A"; "B"; "B"], 'VariableNames', {'Score', 'Group'})`. Which command correctly extracts the 'Score' value from the row where 'Group' is equal to "A"?
- T.Score(T.Group == "A") (Correct answer)
- T('A', 'Score')
- T{T.Group("A"), 'Score'}
- T(1, 1)
Correct answer: T.Score(T.Group == "A")
The expression `T.Group == "A"` creates a logical index `[1; 0; 0]`. Using this logical index to index into the 'Score' variable `T.Score` correctly selects only the elements where the condition is true, returning the value `8`.
Question 6: A financial analyst has two `datetime` objects: `d1 = datetime('2025-01-10');` and `d2 = datetime('2025-03-15');`. To find the total number of calendar days that have passed between these two dates, which is the most direct command?
- days(d2 - d1)
- caldays(d2 - d1)
- d2 - d1 (Correct answer)
- between(d1, d2)
Correct answer: d2 - d1
Directly subtracting one datetime object from another (`d2 - d1`) results in a `duration` object that represents the exact time elapsed. For dates without a time component, this duration is conveniently expressed in days. While other functions can work, direct subtraction is the most fundamental operation for this task.
