Conditional Statements

• Write functions containing if and else statements

live notes

Announcements:

• Midterm next week
• This week’s homework will be to create a midterm review video, details TBA

Plan:

• if statements
• Group reflect activity on data science panel

123 GO - Word summarizing impression of Friday’s data science panel

Conditional statements

# if(CONDITION){
#   DO SOMETHING
# }

x = 2
if(x < 10){
  # Beginning of a block - 123 GO - how many lines of code INSIDE this block?
  print("x is less than 10!")  # line 1
  y = 100       # line 2
}

Define block

else

x = 2

# Predict: Will we see "something else" printed out? 123 GO yes, no, idk
if(x < 10){
  print("x is less than 10!")
  y = 100
} else {
  print("something else!")
}

x = 20

# Predict: Will we see "something else" printed out? 123 GO yes, no, idk
if(x < 10){
  print("x is less than 10!")
  y = 100
} else {
  print("something else!")
}

x = 20

# Predict: Will we see "something else" printed out? 123 GO yes, no, idk
if(x < 10){
  print("x is less than 10!")
  y = 100
} else if (x < 100){
  # x < 100
  print("10 <= x < 100")
} else {
  print("something else!")
}

Nesting

x = 20

if(x < 10){
  print("x is less than 10!") # no
  y = 100
} else if (x < 100){
  # x < 100
  print("10 <= x < 100") # yes
  if (x %% 2 == 0){
    print("x is even") # yes
    if (90 < x){ # This `if` is nested three deep
      print("x is greater than 90") # no
    }
  }
} else {
  print("something else!") # no
}

Moral: Deeply nested code can be difficult to read, so avoid when possible.

ifelse is a function that does everything all at once. Specific purpose- select elementwise from 2 vectors. Use ifelse if you have a long vector of TRUE and FALSE.

In contrast, if and else are used for control flow. In the case of if(CONDITION), CONDITION should have length 1, and should be TRUE or FALSE. Otherwise, it’s probably a mistake.

a = c(TRUE, FALSE) # ambiguous
if(a){
  print("hello!")
}

ifelse(a, "This element TRUE", "This element FALSE")

Assignment

x = 20

if(x < 10){
  y = TRUE
} else {
  y = FALSE
}

# Equivalently

y = if(x < 10){
  TRUE
} else {
  FALSE
}

# 123 GO - what will the value of y?
y

Group activity

15 minutes to reflect and talk with your group about Friday’s data science panel. Use the following questions as a starting place:

1. What were your takeaways?
2. Did it give you any ideas?
3. We have some flexibility later in this class- what would you like to see?

Two people with names appearing last in each group will share- pick one of the questions above, or just general thoughts are fine.

• Impress people with beautiful graphics
• Blog post for your project / showcase work, outside projects
• Looking for problem solving ability
• Propensity to learn
• Defining the actual problem!
• Job opportunities in different fields- wide breadth of opportunities
• Remote work possible
• Encouraging to see people from diverse backgrounds making their way in the field
• +1 Could learn SQL, Python