Lecture 2 - Algorithms to Functions

Question 1

What kind of statement is used for a single condition?

Answer 1

If statement

Question 2

What statement is used for multiple conditions?

Answer 2

If else statement

Question 3

What statements are used in nested conditions?

Answer 3

Multiple if else statements

Question 4

What function is used in Multibranch condition?

Answer 4

Switch( )

Question 5

What kind of loop is used when iterations are known from outset?

Answer 5

For loop

Question 6

What kind of loop is used when iterations are unknown at outset?

Answer 6

While loop, repeat loop

Question 7

What is vectorisation?

Answer 7

Implicit Iteration
e.g.
bob

Question 8

What is the apply function for?

Answer 8

The apply function can be used to apply the same function for example to some large dataset by iterating down a certain column to calculate the same summary statistic

Question 9

Vectorised Conditional Statement

Answer 9

Acts upon a vector like data structure conditional tests upon each element

Question 10

What is a function?

Answer 10

Compartmentalised and reusable blocks of code

Question 11

What is an argument?

Answer 11

Information entering a function.
Good practice to have names.
Can be defined in any order

Question 12

How do you set a default for an argument?

Answer 12

Assign a value to the argument when the function is defined.

Question 13

What is the principle of least privilege?

Answer 13

By encapsulating in a function user does not make changes to objects outwith the function.

Question 14

What is the DRY principle?

Answer 14

Don’t repeat yourself

Question 15

What are the two different methods to make arguments available to functions?

Answer 15

• Pass by value

- Pass by reference

Question 16

What is pass by value?

Answer 16

A copy is made of each object being sent into the function.
Memory address of object in the function environment differs from object address in calling environment.
Changes made to the object while inside the function does not change the objects value in the calling environment.

Question 17

What is pass by reference?

Answer 17

The address of the object is sent into the function.

Any changes made to the object in the function is reflected in the calling environment

Question 18

Pros and cons of pass by value

Answer 18

Pro:
Safer - changes made inside the function are not reflected outside the function.
Con:
Inefficient - copy of information needs to be made to store information in two memory locations.

Question 19

Pros and cons of pass by reference

Answer 19

Pro -
More efficient - doesn’t need to make copy of info to store in different locations
Con -
More dangerous

Question 20

Pure functions

Answer 20

Do not have side effects.

Always map same input into to same output and otherwise leave calling environment unaltered.

Question 21

3 examples of impure functions

Answer 21

library( ) - if a function loads a package, it remains loaded.
setwd( ) - persistent effect after function finishes
par( ) - graphical parameter changes persist.

Question 22

How to make impure functions pure?

Answer 22

using the function on.exit( ) will restore previous state when function finishes

Question 23

Are the arguments for standard functions in R pass by value or pass by reference?

Answer 23

Pass by value